[PATCH] capabilities: audit capability use

[PATCH] capabilities: audit capability use

[Topi Miettinen]

There are many basic ways to control processes, including capabilities,
cgroups and resource limits. However, there are far fewer ways to find
out useful values for the limits, except blind trial and error.

Currently, there is no way to know which capabilities are actually used.
Even the source code is only implicit, in-depth knowledge of each
capability must be used when analyzing a program to judge which
capabilities the program will exercise.

Generate an audit message at system call exit, when capabilities are used.
This can then be used to configure capability sets for services by a
software developer, maintainer or system administrator.

Test case demonstrating basic capability monitoring with the new
message types 1330 and 1331 and how the cgroups are displayed (boot to
rdshell):

BusyBox v1.22.1 (Debian 1:1.22.0-19) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) cd /sys/fs
(initramfs) mount -t cgroup2 cgroup cgroup
[   12.343152] audit_printk_skb: 5886 callbacks suppressed
[   12.355214] audit: type=1300 audit(1468234317.100:518): arch=c000003e syscall=165 success=yes exit=0 a0=7fffe1e9ae2d a1=7fffe1e9ae34 a2=7fffe1e9ae25 a3=8000 items=0 ppid=469 pid=470 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mount" exe="/bin/mount" key=(null)
[   12.414853] audit: type=1327 audit(1468234317.100:518): proctitle=6D6F756E74002D74006367726F757032006367726F7570006367726F7570
[   12.438338] audit: type=1330 audit(1468234317.100:518): cap_used=0000000000200000
[   12.453893] audit: type=1331 audit(1468234317.100:518): cgroups=:/;
(initramfs) cd cgroup
(initramfs) mkdir test; cd test
[   17.335625] audit: type=1300 audit(1468234322.092:519): arch=c000003e syscall=83 success=yes exit=0 a0=7ffddfd75e29 a1=1ff a2=0 a3=1e2 items=0 ppid=469 pid=471 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mkdir" exe="/bin/mkdir" key=(null)
[   17.392686] audit: type=1327 audit(1468234322.092:519): proctitle=6D6B6469720074657374
[   17.409404] audit: type=1330 audit(1468234322.092:519): cap_used=0000000000000002
[   17.425404] audit: type=1331 audit(1468234322.092:519): cgroups=:/;
(initramfs) echo $$ >cgroup.procs
(initramfs) mknod /dev/z_$$ c 1 2
[   28.385681] audit: type=1300 audit(1468234333.144:520): arch=c000003e syscall=133 success=yes exit=0 a0=7ffe16324e11 a1=21b6 a2=102 a3=5c9 items=0 ppid=469 pid=472 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mknod" exe="/bin/mknod" key=(null)
[   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
[   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
[   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;
(initramfs) chown 1234 /dev/z_*
[   34.772992] audit: type=1300 audit(1468234339.532:521): arch=c000003e syscall=92 success=yes exit=0 a0=7ffd0b563e17 a1=4d2 a2=0 a3=60a items=0 ppid=469 pid=473 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="chown" exe="/bin/chown" key=(null)
[   34.828569] audit: type=1327 audit(1468234339.532:521): proctitle=63686F776E0031323334002F6465762F7A5F343639
[   34.848747] audit: type=1330 audit(1468234339.532:521): cap_used=0000000000000001
[   34.864404] audit: type=1331 audit(1468234339.532:521): cgroups=:/test;

Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
---
 include/linux/audit.h      |  4 +++
 include/linux/cgroup.h     |  2 ++
 include/uapi/linux/audit.h |  2 ++
 kernel/audit.c             |  7 +++---
 kernel/audit.h             |  1 +
 kernel/auditsc.c           | 28 ++++++++++++++++++++-
 kernel/capability.c        |  5 ++--
 kernel/cgroup.c            | 62 ++++++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 105 insertions(+), 6 deletions(-)

diff --git a/include/linux/audit.h b/include/linux/audit.h
index e38e3fc..971cb2e 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -438,6 +438,8 @@ static inline void audit_mmap_fd(int fd, int flags)
 		__audit_mmap_fd(fd, flags);
 }
 
+extern void audit_log_cap_use(int cap);
+
 extern int audit_n_rules;
 extern int audit_signals;
 #else /* CONFIG_AUDITSYSCALL */
@@ -545,6 +547,8 @@ static inline void audit_mmap_fd(int fd, int flags)
 { }
 static inline void audit_ptrace(struct task_struct *t)
 { }
+static inline void audit_log_cap_use(int cap)
+{ }
 #define audit_n_rules 0
 #define audit_signals 0
 #endif /* CONFIG_AUDITSYSCALL */
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a20320c..b5dc8aa 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -100,6 +100,8 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
 int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		     struct pid *pid, struct task_struct *tsk);
+struct audit_buffer;
+void audit_cgroup_list(struct audit_buffer *ab);
 
 void cgroup_fork(struct task_struct *p);
 extern int cgroup_can_fork(struct task_struct *p);
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index d820aa9..c1ae016 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -111,6 +111,8 @@
 #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
 #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
 #define AUDIT_REPLACE		1329	/* Replace auditd if this packet unanswerd */
+#define AUDIT_CAPABILITY	1330	/* Record showing capability use */
+#define AUDIT_CGROUP		1331	/* Record showing cgroups */
 
 #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
 #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
diff --git a/kernel/audit.c b/kernel/audit.c
index 8d528f9..98dd920 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -54,6 +54,7 @@
 #include <linux/kthread.h>
 #include <linux/kernel.h>
 #include <linux/syscalls.h>
+#include <linux/cgroup.h>
 
 #include <linux/audit.h>
 
@@ -1682,7 +1683,7 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
 {
 	int i;
 
-	audit_log_format(ab, " %s=", prefix);
+	audit_log_format(ab, "%s=", prefix);
 	CAP_FOR_EACH_U32(i) {
 		audit_log_format(ab, "%08x",
 				 cap->cap[CAP_LAST_U32 - i]);
@@ -1696,11 +1697,11 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
 	int log = 0;
 
 	if (!cap_isclear(*perm)) {
-		audit_log_cap(ab, "cap_fp", perm);
+		audit_log_cap(ab, " cap_fp", perm);
 		log = 1;
 	}
 	if (!cap_isclear(*inh)) {
-		audit_log_cap(ab, "cap_fi", inh);
+		audit_log_cap(ab, " cap_fi", inh);
 		log = 1;
 	}
 
diff --git a/kernel/audit.h b/kernel/audit.h
index a492f4c..680e8b5 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -202,6 +202,7 @@ struct audit_context {
 	};
 	int fds[2];
 	struct audit_proctitle proctitle;
+	kernel_cap_t cap_used;
 };
 
 extern u32 audit_ever_enabled;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 2672d10..32c3813 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -197,7 +197,6 @@ static int audit_match_filetype(struct audit_context *ctx, int val)
  * References in it _are_ dropped - at the same time we free/drop aux stuff.
  */
 
-#ifdef CONFIG_AUDIT_TREE
 static void audit_set_auditable(struct audit_context *ctx)
 {
 	if (!ctx->prio) {
@@ -206,6 +205,7 @@ static void audit_set_auditable(struct audit_context *ctx)
 	}
 }
 
+#ifdef CONFIG_AUDIT_TREE
 static int put_tree_ref(struct audit_context *ctx, struct audit_chunk *chunk)
 {
 	struct audit_tree_refs *p = ctx->trees;
@@ -1439,6 +1439,18 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 
 	audit_log_proctitle(tsk, context);
 
+	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
+	if (ab) {
+		audit_log_cap(ab, "cap_used", &context->cap_used);
+		audit_log_end(ab);
+	}
+	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CGROUP);
+	if (ab) {
+		audit_log_format(ab, "cgroups=");
+		audit_cgroup_list(ab);
+		audit_log_end(ab);
+	}
+
 	/* Send end of event record to help user space know we are finished */
 	ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
 	if (ab)
@@ -2428,3 +2440,17 @@ struct list_head *audit_killed_trees(void)
 		return NULL;
 	return &ctx->killed_trees;
 }
+
+void audit_log_cap_use(int cap)
+{
+	struct audit_context *context = current->audit_context;
+
+	if (context) {
+		cap_raise(context->cap_used, cap);
+		audit_set_auditable(context);
+	} else {
+		audit_log(NULL, GFP_NOFS, AUDIT_CAPABILITY,
+			  "cap_used=%d pid=%d no audit_context",
+			  cap, task_pid_nr(current));
+	}
+}
diff --git a/kernel/capability.c b/kernel/capability.c
index 45432b5..d45d5b1 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -366,8 +366,8 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
  * @ns:  The usernamespace we want the capability in
  * @cap: The capability to be tested for
  *
- * Return true if the current task has the given superior capability currently
- * available for use, false if not.
+ * Return true if the current task has the given superior capability
+ * currently available for use, false if not. Write an audit message.
  *
  * This sets PF_SUPERPRIV on the task if the capability is available on the
  * assumption that it's about to be used.
@@ -380,6 +380,7 @@ bool ns_capable(struct user_namespace *ns, int cap)
 	}
 
 	if (security_capable(current_cred(), ns, cap) == 0) {
+		audit_log_cap_use(cap);
 		current->flags |= PF_SUPERPRIV;
 		return true;
 	}
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 75c0ff0..1931679 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -63,6 +63,7 @@
 #include <linux/nsproxy.h>
 #include <linux/proc_ns.h>
 #include <net/sock.h>
+#include <linux/audit.h>
 
 /*
  * pidlists linger the following amount before being destroyed.  The goal
@@ -5789,6 +5790,67 @@ out:
 	return retval;
 }
 
+/*
+ * audit_cgroup_list()
+ *  - Print task's cgroup paths with audit_log_format()
+ *  - Used for capability audit logging
+ *  - Otherwise very similar to proc_cgroup_show().
+ */
+void audit_cgroup_list(struct audit_buffer *ab)
+{
+	char *buf, *path;
+	struct cgroup_root *root;
+
+	buf = kmalloc(PATH_MAX, GFP_NOFS);
+	if (!buf)
+		return;
+
+	mutex_lock(&cgroup_mutex);
+	spin_lock_irq(&css_set_lock);
+
+	for_each_root(root) {
+		struct cgroup_subsys *ss;
+		struct cgroup *cgrp;
+		int ssid, count = 0;
+
+		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
+			continue;
+
+		if (root != &cgrp_dfl_root)
+			for_each_subsys(ss, ssid)
+				if (root->subsys_mask & (1 << ssid))
+					audit_log_format(ab, "%s%s",
+							 count++ ? "," : "",
+							 ss->legacy_name);
+		if (strlen(root->name))
+			audit_log_format(ab, "%sname=%s", count ? "," : "",
+					 root->name);
+		audit_log_format(ab, ":");
+
+		cgrp = task_cgroup_from_root(current, root);
+
+		if (cgroup_on_dfl(cgrp) || !(current->flags & PF_EXITING)) {
+			path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
+						current->nsproxy->cgroup_ns);
+			if (!path)
+				goto out_unlock;
+		} else
+			path = "/";
+
+		audit_log_format(ab, "%s", path);
+
+		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
+			audit_log_format(ab, " (deleted);");
+		else
+			audit_log_format(ab, ";");
+	}
+
+out_unlock:
+	spin_unlock_irq(&css_set_lock);
+	mutex_unlock(&cgroup_mutex);
+	kfree(buf);
+}
+
 /* Display information about each subsystem and each hierarchy */
 static int proc_cgroupstats_show(struct seq_file *m, void *v)
 {
-- 
2.8.1

Re: [PATCH] capabilities: audit capability use

[Serge E. Hallyn]

Quoting Topi Miettinen (toiwoton@gmail.com):
> There are many basic ways to control processes, including capabilities,
> cgroups and resource limits. However, there are far fewer ways to find
> out useful values for the limits, except blind trial and error.
> 
> Currently, there is no way to know which capabilities are actually used.
> Even the source code is only implicit, in-depth knowledge of each
> capability must be used when analyzing a program to judge which
> capabilities the program will exercise.
> 
> Generate an audit message at system call exit, when capabilities are used.
> This can then be used to configure capability sets for services by a
> software developer, maintainer or system administrator.
> 
> Test case demonstrating basic capability monitoring with the new
> message types 1330 and 1331 and how the cgroups are displayed (boot to
> rdshell):

Thanks, Topi, I'll find time this week to look this over in detail.

How much chattier does this make the syslog/journald during a regular
boot?  I was thinking "this is audit, we can choose what messages
will show up", but I guess that' sonly what auditd actually listens to,
not what kernel emits?  (sorry i've not looked at audit in a long
time).  Drat, that makes it seem like tracepoints would be better
after all.  But let's see how much it addes to the noise.

> BusyBox v1.22.1 (Debian 1:1.22.0-19) built-in shell (ash)
> Enter 'help' for a list of built-in commands.
> 
> (initramfs) cd /sys/fs
> (initramfs) mount -t cgroup2 cgroup cgroup
> [   12.343152] audit_printk_skb: 5886 callbacks suppressed
> [   12.355214] audit: type=1300 audit(1468234317.100:518): arch=c000003e syscall=165 success=yes exit=0 a0=7fffe1e9ae2d a1=7fffe1e9ae34 a2=7fffe1e9ae25 a3=8000 items=0 ppid=469 pid=470 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mount" exe="/bin/mount" key=(null)
> [   12.414853] audit: type=1327 audit(1468234317.100:518): proctitle=6D6F756E74002D74006367726F757032006367726F7570006367726F7570
> [   12.438338] audit: type=1330 audit(1468234317.100:518): cap_used=0000000000200000
> [   12.453893] audit: type=1331 audit(1468234317.100:518): cgroups=:/;
> (initramfs) cd cgroup
> (initramfs) mkdir test; cd test
> [   17.335625] audit: type=1300 audit(1468234322.092:519): arch=c000003e syscall=83 success=yes exit=0 a0=7ffddfd75e29 a1=1ff a2=0 a3=1e2 items=0 ppid=469 pid=471 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mkdir" exe="/bin/mkdir" key=(null)
> [   17.392686] audit: type=1327 audit(1468234322.092:519): proctitle=6D6B6469720074657374
> [   17.409404] audit: type=1330 audit(1468234322.092:519): cap_used=0000000000000002
> [   17.425404] audit: type=1331 audit(1468234322.092:519): cgroups=:/;
> (initramfs) echo $$ >cgroup.procs
> (initramfs) mknod /dev/z_$$ c 1 2
> [   28.385681] audit: type=1300 audit(1468234333.144:520): arch=c000003e syscall=133 success=yes exit=0 a0=7ffe16324e11 a1=21b6 a2=102 a3=5c9 items=0 ppid=469 pid=472 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mknod" exe="/bin/mknod" key=(null)
> [   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
> [   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
> [   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;
> (initramfs) chown 1234 /dev/z_*
> [   34.772992] audit: type=1300 audit(1468234339.532:521): arch=c000003e syscall=92 success=yes exit=0 a0=7ffd0b563e17 a1=4d2 a2=0 a3=60a items=0 ppid=469 pid=473 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="chown" exe="/bin/chown" key=(null)
> [   34.828569] audit: type=1327 audit(1468234339.532:521): proctitle=63686F776E0031323334002F6465762F7A5F343639
> [   34.848747] audit: type=1330 audit(1468234339.532:521): cap_used=0000000000000001
> [   34.864404] audit: type=1331 audit(1468234339.532:521): cgroups=:/test;
> 
> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
> ---
>  include/linux/audit.h      |  4 +++
>  include/linux/cgroup.h     |  2 ++
>  include/uapi/linux/audit.h |  2 ++
>  kernel/audit.c             |  7 +++---
>  kernel/audit.h             |  1 +
>  kernel/auditsc.c           | 28 ++++++++++++++++++++-
>  kernel/capability.c        |  5 ++--
>  kernel/cgroup.c            | 62 ++++++++++++++++++++++++++++++++++++++++++++++
>  8 files changed, 105 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index e38e3fc..971cb2e 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -438,6 +438,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>  		__audit_mmap_fd(fd, flags);
>  }
>  
> +extern void audit_log_cap_use(int cap);
> +
>  extern int audit_n_rules;
>  extern int audit_signals;
>  #else /* CONFIG_AUDITSYSCALL */
> @@ -545,6 +547,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>  { }
>  static inline void audit_ptrace(struct task_struct *t)
>  { }
> +static inline void audit_log_cap_use(int cap)
> +{ }
>  #define audit_n_rules 0
>  #define audit_signals 0
>  #endif /* CONFIG_AUDITSYSCALL */
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index a20320c..b5dc8aa 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -100,6 +100,8 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
>  int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
>  int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
>  		     struct pid *pid, struct task_struct *tsk);
> +struct audit_buffer;
> +void audit_cgroup_list(struct audit_buffer *ab);
>  
>  void cgroup_fork(struct task_struct *p);
>  extern int cgroup_can_fork(struct task_struct *p);
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index d820aa9..c1ae016 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -111,6 +111,8 @@
>  #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
>  #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
>  #define AUDIT_REPLACE		1329	/* Replace auditd if this packet unanswerd */
> +#define AUDIT_CAPABILITY	1330	/* Record showing capability use */
> +#define AUDIT_CGROUP		1331	/* Record showing cgroups */
>  
>  #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
>  #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 8d528f9..98dd920 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -54,6 +54,7 @@
>  #include <linux/kthread.h>
>  #include <linux/kernel.h>
>  #include <linux/syscalls.h>
> +#include <linux/cgroup.h>
>  
>  #include <linux/audit.h>
>  
> @@ -1682,7 +1683,7 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
>  {
>  	int i;
>  
> -	audit_log_format(ab, " %s=", prefix);
> +	audit_log_format(ab, "%s=", prefix);
>  	CAP_FOR_EACH_U32(i) {
>  		audit_log_format(ab, "%08x",
>  				 cap->cap[CAP_LAST_U32 - i]);
> @@ -1696,11 +1697,11 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
>  	int log = 0;
>  
>  	if (!cap_isclear(*perm)) {
> -		audit_log_cap(ab, "cap_fp", perm);
> +		audit_log_cap(ab, " cap_fp", perm);
>  		log = 1;
>  	}
>  	if (!cap_isclear(*inh)) {
> -		audit_log_cap(ab, "cap_fi", inh);
> +		audit_log_cap(ab, " cap_fi", inh);
>  		log = 1;
>  	}
>  
> diff --git a/kernel/audit.h b/kernel/audit.h
> index a492f4c..680e8b5 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -202,6 +202,7 @@ struct audit_context {
>  	};
>  	int fds[2];
>  	struct audit_proctitle proctitle;
> +	kernel_cap_t cap_used;
>  };
>  
>  extern u32 audit_ever_enabled;
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 2672d10..32c3813 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -197,7 +197,6 @@ static int audit_match_filetype(struct audit_context *ctx, int val)
>   * References in it _are_ dropped - at the same time we free/drop aux stuff.
>   */
>  
> -#ifdef CONFIG_AUDIT_TREE
>  static void audit_set_auditable(struct audit_context *ctx)
>  {
>  	if (!ctx->prio) {
> @@ -206,6 +205,7 @@ static void audit_set_auditable(struct audit_context *ctx)
>  	}
>  }
>  
> +#ifdef CONFIG_AUDIT_TREE
>  static int put_tree_ref(struct audit_context *ctx, struct audit_chunk *chunk)
>  {
>  	struct audit_tree_refs *p = ctx->trees;
> @@ -1439,6 +1439,18 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
>  
>  	audit_log_proctitle(tsk, context);
>  
> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
> +	if (ab) {
> +		audit_log_cap(ab, "cap_used", &context->cap_used);
> +		audit_log_end(ab);
> +	}
> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CGROUP);
> +	if (ab) {
> +		audit_log_format(ab, "cgroups=");
> +		audit_cgroup_list(ab);
> +		audit_log_end(ab);
> +	}
> +
>  	/* Send end of event record to help user space know we are finished */
>  	ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
>  	if (ab)
> @@ -2428,3 +2440,17 @@ struct list_head *audit_killed_trees(void)
>  		return NULL;
>  	return &ctx->killed_trees;
>  }
> +
> +void audit_log_cap_use(int cap)
> +{
> +	struct audit_context *context = current->audit_context;
> +
> +	if (context) {
> +		cap_raise(context->cap_used, cap);
> +		audit_set_auditable(context);
> +	} else {
> +		audit_log(NULL, GFP_NOFS, AUDIT_CAPABILITY,
> +			  "cap_used=%d pid=%d no audit_context",
> +			  cap, task_pid_nr(current));
> +	}
> +}
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 45432b5..d45d5b1 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -366,8 +366,8 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>   * @ns:  The usernamespace we want the capability in
>   * @cap: The capability to be tested for
>   *
> - * Return true if the current task has the given superior capability currently
> - * available for use, false if not.
> + * Return true if the current task has the given superior capability
> + * currently available for use, false if not. Write an audit message.
>   *
>   * This sets PF_SUPERPRIV on the task if the capability is available on the
>   * assumption that it's about to be used.
> @@ -380,6 +380,7 @@ bool ns_capable(struct user_namespace *ns, int cap)
>  	}
>  
>  	if (security_capable(current_cred(), ns, cap) == 0) {
> +		audit_log_cap_use(cap);
>  		current->flags |= PF_SUPERPRIV;
>  		return true;
>  	}
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 75c0ff0..1931679 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -63,6 +63,7 @@
>  #include <linux/nsproxy.h>
>  #include <linux/proc_ns.h>
>  #include <net/sock.h>
> +#include <linux/audit.h>
>  
>  /*
>   * pidlists linger the following amount before being destroyed.  The goal
> @@ -5789,6 +5790,67 @@ out:
>  	return retval;
>  }
>  
> +/*
> + * audit_cgroup_list()
> + *  - Print task's cgroup paths with audit_log_format()
> + *  - Used for capability audit logging
> + *  - Otherwise very similar to proc_cgroup_show().
> + */
> +void audit_cgroup_list(struct audit_buffer *ab)
> +{
> +	char *buf, *path;
> +	struct cgroup_root *root;
> +
> +	buf = kmalloc(PATH_MAX, GFP_NOFS);
> +	if (!buf)
> +		return;
> +
> +	mutex_lock(&cgroup_mutex);
> +	spin_lock_irq(&css_set_lock);
> +
> +	for_each_root(root) {
> +		struct cgroup_subsys *ss;
> +		struct cgroup *cgrp;
> +		int ssid, count = 0;
> +
> +		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
> +			continue;
> +
> +		if (root != &cgrp_dfl_root)
> +			for_each_subsys(ss, ssid)
> +				if (root->subsys_mask & (1 << ssid))
> +					audit_log_format(ab, "%s%s",
> +							 count++ ? "," : "",
> +							 ss->legacy_name);
> +		if (strlen(root->name))
> +			audit_log_format(ab, "%sname=%s", count ? "," : "",
> +					 root->name);
> +		audit_log_format(ab, ":");
> +
> +		cgrp = task_cgroup_from_root(current, root);
> +
> +		if (cgroup_on_dfl(cgrp) || !(current->flags & PF_EXITING)) {
> +			path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
> +						current->nsproxy->cgroup_ns);
> +			if (!path)
> +				goto out_unlock;
> +		} else
> +			path = "/";
> +
> +		audit_log_format(ab, "%s", path);
> +
> +		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
> +			audit_log_format(ab, " (deleted);");
> +		else
> +			audit_log_format(ab, ";");
> +	}
> +
> +out_unlock:
> +	spin_unlock_irq(&css_set_lock);
> +	mutex_unlock(&cgroup_mutex);
> +	kfree(buf);
> +}
> +
>  /* Display information about each subsystem and each hierarchy */
>  static int proc_cgroupstats_show(struct seq_file *m, void *v)
>  {
> -- 
> 2.8.1

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/11/16 15:25, Serge E. Hallyn wrote:
> Quoting Topi Miettinen (toiwoton@gmail.com):
>> There are many basic ways to control processes, including capabilities,
>> cgroups and resource limits. However, there are far fewer ways to find
>> out useful values for the limits, except blind trial and error.
>>
>> Currently, there is no way to know which capabilities are actually used.
>> Even the source code is only implicit, in-depth knowledge of each
>> capability must be used when analyzing a program to judge which
>> capabilities the program will exercise.
>>
>> Generate an audit message at system call exit, when capabilities are used.
>> This can then be used to configure capability sets for services by a
>> software developer, maintainer or system administrator.
>>
>> Test case demonstrating basic capability monitoring with the new
>> message types 1330 and 1331 and how the cgroups are displayed (boot to
>> rdshell):
> 
> Thanks, Topi, I'll find time this week to look this over in detail.
> 
> How much chattier does this make the syslog/journald during a regular
> boot?  I was thinking "this is audit, we can choose what messages
> will show up", but I guess that' sonly what auditd actually listens to,
> not what kernel emits?  (sorry i've not looked at audit in a long
> time).  Drat, that makes it seem like tracepoints would be better
> after all.  But let's see how much it addes to the noise.

For example "loadkeys" causes thousands of entries. :-( I'm checking how
to avoid audit message rate limiting, now some messages are lost.

It's still too easy to drown the logs with noise. That could be limited
a lot by emitting a message only when the capability is used for the
first time. But the question is how to define where to start counting
(fork, exec, and/or setpcap?). I'm also not sure if that is the right
way to log, since the first use of a capability could be expected and an
innocent one, but then the 100th one could be malicious.

It's also very complex and error-prone to collect a capability mask from
audit logs, which was my original goal.

-Topi

> 
>> BusyBox v1.22.1 (Debian 1:1.22.0-19) built-in shell (ash)
>> Enter 'help' for a list of built-in commands.
>>
>> (initramfs) cd /sys/fs
>> (initramfs) mount -t cgroup2 cgroup cgroup
>> [   12.343152] audit_printk_skb: 5886 callbacks suppressed
>> [   12.355214] audit: type=1300 audit(1468234317.100:518): arch=c000003e syscall=165 success=yes exit=0 a0=7fffe1e9ae2d a1=7fffe1e9ae34 a2=7fffe1e9ae25 a3=8000 items=0 ppid=469 pid=470 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mount" exe="/bin/mount" key=(null)
>> [   12.414853] audit: type=1327 audit(1468234317.100:518): proctitle=6D6F756E74002D74006367726F757032006367726F7570006367726F7570
>> [   12.438338] audit: type=1330 audit(1468234317.100:518): cap_used=0000000000200000
>> [   12.453893] audit: type=1331 audit(1468234317.100:518): cgroups=:/;
>> (initramfs) cd cgroup
>> (initramfs) mkdir test; cd test
>> [   17.335625] audit: type=1300 audit(1468234322.092:519): arch=c000003e syscall=83 success=yes exit=0 a0=7ffddfd75e29 a1=1ff a2=0 a3=1e2 items=0 ppid=469 pid=471 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mkdir" exe="/bin/mkdir" key=(null)
>> [   17.392686] audit: type=1327 audit(1468234322.092:519): proctitle=6D6B6469720074657374
>> [   17.409404] audit: type=1330 audit(1468234322.092:519): cap_used=0000000000000002
>> [   17.425404] audit: type=1331 audit(1468234322.092:519): cgroups=:/;
>> (initramfs) echo $$ >cgroup.procs
>> (initramfs) mknod /dev/z_$$ c 1 2
>> [   28.385681] audit: type=1300 audit(1468234333.144:520): arch=c000003e syscall=133 success=yes exit=0 a0=7ffe16324e11 a1=21b6 a2=102 a3=5c9 items=0 ppid=469 pid=472 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mknod" exe="/bin/mknod" key=(null)
>> [   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
>> [   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
>> [   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;
>> (initramfs) chown 1234 /dev/z_*
>> [   34.772992] audit: type=1300 audit(1468234339.532:521): arch=c000003e syscall=92 success=yes exit=0 a0=7ffd0b563e17 a1=4d2 a2=0 a3=60a items=0 ppid=469 pid=473 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="chown" exe="/bin/chown" key=(null)
>> [   34.828569] audit: type=1327 audit(1468234339.532:521): proctitle=63686F776E0031323334002F6465762F7A5F343639
>> [   34.848747] audit: type=1330 audit(1468234339.532:521): cap_used=0000000000000001
>> [   34.864404] audit: type=1331 audit(1468234339.532:521): cgroups=:/test;
>>
>> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
>> ---
>>  include/linux/audit.h      |  4 +++
>>  include/linux/cgroup.h     |  2 ++
>>  include/uapi/linux/audit.h |  2 ++
>>  kernel/audit.c             |  7 +++---
>>  kernel/audit.h             |  1 +
>>  kernel/auditsc.c           | 28 ++++++++++++++++++++-
>>  kernel/capability.c        |  5 ++--
>>  kernel/cgroup.c            | 62 ++++++++++++++++++++++++++++++++++++++++++++++
>>  8 files changed, 105 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/audit.h b/include/linux/audit.h
>> index e38e3fc..971cb2e 100644
>> --- a/include/linux/audit.h
>> +++ b/include/linux/audit.h
>> @@ -438,6 +438,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>>  		__audit_mmap_fd(fd, flags);
>>  }
>>  
>> +extern void audit_log_cap_use(int cap);
>> +
>>  extern int audit_n_rules;
>>  extern int audit_signals;
>>  #else /* CONFIG_AUDITSYSCALL */
>> @@ -545,6 +547,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>>  { }
>>  static inline void audit_ptrace(struct task_struct *t)
>>  { }
>> +static inline void audit_log_cap_use(int cap)
>> +{ }
>>  #define audit_n_rules 0
>>  #define audit_signals 0
>>  #endif /* CONFIG_AUDITSYSCALL */
>> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
>> index a20320c..b5dc8aa 100644
>> --- a/include/linux/cgroup.h
>> +++ b/include/linux/cgroup.h
>> @@ -100,6 +100,8 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
>>  int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
>>  int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
>>  		     struct pid *pid, struct task_struct *tsk);
>> +struct audit_buffer;
>> +void audit_cgroup_list(struct audit_buffer *ab);
>>  
>>  void cgroup_fork(struct task_struct *p);
>>  extern int cgroup_can_fork(struct task_struct *p);
>> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
>> index d820aa9..c1ae016 100644
>> --- a/include/uapi/linux/audit.h
>> +++ b/include/uapi/linux/audit.h
>> @@ -111,6 +111,8 @@
>>  #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
>>  #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
>>  #define AUDIT_REPLACE		1329	/* Replace auditd if this packet unanswerd */
>> +#define AUDIT_CAPABILITY	1330	/* Record showing capability use */
>> +#define AUDIT_CGROUP		1331	/* Record showing cgroups */
>>  
>>  #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
>>  #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
>> diff --git a/kernel/audit.c b/kernel/audit.c
>> index 8d528f9..98dd920 100644
>> --- a/kernel/audit.c
>> +++ b/kernel/audit.c
>> @@ -54,6 +54,7 @@
>>  #include <linux/kthread.h>
>>  #include <linux/kernel.h>
>>  #include <linux/syscalls.h>
>> +#include <linux/cgroup.h>
>>  
>>  #include <linux/audit.h>
>>  
>> @@ -1682,7 +1683,7 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
>>  {
>>  	int i;
>>  
>> -	audit_log_format(ab, " %s=", prefix);
>> +	audit_log_format(ab, "%s=", prefix);
>>  	CAP_FOR_EACH_U32(i) {
>>  		audit_log_format(ab, "%08x",
>>  				 cap->cap[CAP_LAST_U32 - i]);
>> @@ -1696,11 +1697,11 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
>>  	int log = 0;
>>  
>>  	if (!cap_isclear(*perm)) {
>> -		audit_log_cap(ab, "cap_fp", perm);
>> +		audit_log_cap(ab, " cap_fp", perm);
>>  		log = 1;
>>  	}
>>  	if (!cap_isclear(*inh)) {
>> -		audit_log_cap(ab, "cap_fi", inh);
>> +		audit_log_cap(ab, " cap_fi", inh);
>>  		log = 1;
>>  	}
>>  
>> diff --git a/kernel/audit.h b/kernel/audit.h
>> index a492f4c..680e8b5 100644
>> --- a/kernel/audit.h
>> +++ b/kernel/audit.h
>> @@ -202,6 +202,7 @@ struct audit_context {
>>  	};
>>  	int fds[2];
>>  	struct audit_proctitle proctitle;
>> +	kernel_cap_t cap_used;
>>  };
>>  
>>  extern u32 audit_ever_enabled;
>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>> index 2672d10..32c3813 100644
>> --- a/kernel/auditsc.c
>> +++ b/kernel/auditsc.c
>> @@ -197,7 +197,6 @@ static int audit_match_filetype(struct audit_context *ctx, int val)
>>   * References in it _are_ dropped - at the same time we free/drop aux stuff.
>>   */
>>  
>> -#ifdef CONFIG_AUDIT_TREE
>>  static void audit_set_auditable(struct audit_context *ctx)
>>  {
>>  	if (!ctx->prio) {
>> @@ -206,6 +205,7 @@ static void audit_set_auditable(struct audit_context *ctx)
>>  	}
>>  }
>>  
>> +#ifdef CONFIG_AUDIT_TREE
>>  static int put_tree_ref(struct audit_context *ctx, struct audit_chunk *chunk)
>>  {
>>  	struct audit_tree_refs *p = ctx->trees;
>> @@ -1439,6 +1439,18 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
>>  
>>  	audit_log_proctitle(tsk, context);
>>  
>> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
>> +	if (ab) {
>> +		audit_log_cap(ab, "cap_used", &context->cap_used);
>> +		audit_log_end(ab);
>> +	}
>> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CGROUP);
>> +	if (ab) {
>> +		audit_log_format(ab, "cgroups=");
>> +		audit_cgroup_list(ab);
>> +		audit_log_end(ab);
>> +	}
>> +
>>  	/* Send end of event record to help user space know we are finished */
>>  	ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
>>  	if (ab)
>> @@ -2428,3 +2440,17 @@ struct list_head *audit_killed_trees(void)
>>  		return NULL;
>>  	return &ctx->killed_trees;
>>  }
>> +
>> +void audit_log_cap_use(int cap)
>> +{
>> +	struct audit_context *context = current->audit_context;
>> +
>> +	if (context) {
>> +		cap_raise(context->cap_used, cap);
>> +		audit_set_auditable(context);
>> +	} else {
>> +		audit_log(NULL, GFP_NOFS, AUDIT_CAPABILITY,
>> +			  "cap_used=%d pid=%d no audit_context",
>> +			  cap, task_pid_nr(current));
>> +	}
>> +}
>> diff --git a/kernel/capability.c b/kernel/capability.c
>> index 45432b5..d45d5b1 100644
>> --- a/kernel/capability.c
>> +++ b/kernel/capability.c
>> @@ -366,8 +366,8 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>>   * @ns:  The usernamespace we want the capability in
>>   * @cap: The capability to be tested for
>>   *
>> - * Return true if the current task has the given superior capability currently
>> - * available for use, false if not.
>> + * Return true if the current task has the given superior capability
>> + * currently available for use, false if not. Write an audit message.
>>   *
>>   * This sets PF_SUPERPRIV on the task if the capability is available on the
>>   * assumption that it's about to be used.
>> @@ -380,6 +380,7 @@ bool ns_capable(struct user_namespace *ns, int cap)
>>  	}
>>  
>>  	if (security_capable(current_cred(), ns, cap) == 0) {
>> +		audit_log_cap_use(cap);
>>  		current->flags |= PF_SUPERPRIV;
>>  		return true;
>>  	}
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index 75c0ff0..1931679 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -63,6 +63,7 @@
>>  #include <linux/nsproxy.h>
>>  #include <linux/proc_ns.h>
>>  #include <net/sock.h>
>> +#include <linux/audit.h>
>>  
>>  /*
>>   * pidlists linger the following amount before being destroyed.  The goal
>> @@ -5789,6 +5790,67 @@ out:
>>  	return retval;
>>  }
>>  
>> +/*
>> + * audit_cgroup_list()
>> + *  - Print task's cgroup paths with audit_log_format()
>> + *  - Used for capability audit logging
>> + *  - Otherwise very similar to proc_cgroup_show().
>> + */
>> +void audit_cgroup_list(struct audit_buffer *ab)
>> +{
>> +	char *buf, *path;
>> +	struct cgroup_root *root;
>> +
>> +	buf = kmalloc(PATH_MAX, GFP_NOFS);
>> +	if (!buf)
>> +		return;
>> +
>> +	mutex_lock(&cgroup_mutex);
>> +	spin_lock_irq(&css_set_lock);
>> +
>> +	for_each_root(root) {
>> +		struct cgroup_subsys *ss;
>> +		struct cgroup *cgrp;
>> +		int ssid, count = 0;
>> +
>> +		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
>> +			continue;
>> +
>> +		if (root != &cgrp_dfl_root)
>> +			for_each_subsys(ss, ssid)
>> +				if (root->subsys_mask & (1 << ssid))
>> +					audit_log_format(ab, "%s%s",
>> +							 count++ ? "," : "",
>> +							 ss->legacy_name);
>> +		if (strlen(root->name))
>> +			audit_log_format(ab, "%sname=%s", count ? "," : "",
>> +					 root->name);
>> +		audit_log_format(ab, ":");
>> +
>> +		cgrp = task_cgroup_from_root(current, root);
>> +
>> +		if (cgroup_on_dfl(cgrp) || !(current->flags & PF_EXITING)) {
>> +			path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
>> +						current->nsproxy->cgroup_ns);
>> +			if (!path)
>> +				goto out_unlock;
>> +		} else
>> +			path = "/";
>> +
>> +		audit_log_format(ab, "%s", path);
>> +
>> +		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
>> +			audit_log_format(ab, " (deleted);");
>> +		else
>> +			audit_log_format(ab, ";");
>> +	}
>> +
>> +out_unlock:
>> +	spin_unlock_irq(&css_set_lock);
>> +	mutex_unlock(&cgroup_mutex);
>> +	kfree(buf);
>> +}
>> +
>>  /* Display information about each subsystem and each hierarchy */
>>  static int proc_cgroupstats_show(struct seq_file *m, void *v)
>>  {
>> -- 
>> 2.8.1

Re: [PATCH] capabilities: audit capability use

[Tejun Heo]

Hello,

On Mon, Jul 11, 2016 at 02:14:31PM +0300, Topi Miettinen wrote:
> [   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
> [   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
> [   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;

Please don't put additions of the two different audit types into one
patch and I don't think the cgroup audit logging makes much sense.
Without logging all migrations, it doesn't help auditing all that
much.  Also, printing all cgroup membership like that can be
problematic for audit it can be arbitrarily long.

Thanks.

-- 
tejun

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/11/16 16:05, Topi Miettinen wrote:
> On 07/11/16 15:25, Serge E. Hallyn wrote:
>> Quoting Topi Miettinen (toiwoton@gmail.com):
>>> There are many basic ways to control processes, including capabilities,
>>> cgroups and resource limits. However, there are far fewer ways to find
>>> out useful values for the limits, except blind trial and error.
>>>
>>> Currently, there is no way to know which capabilities are actually used.
>>> Even the source code is only implicit, in-depth knowledge of each
>>> capability must be used when analyzing a program to judge which
>>> capabilities the program will exercise.
>>>
>>> Generate an audit message at system call exit, when capabilities are used.
>>> This can then be used to configure capability sets for services by a
>>> software developer, maintainer or system administrator.
>>>
>>> Test case demonstrating basic capability monitoring with the new
>>> message types 1330 and 1331 and how the cgroups are displayed (boot to
>>> rdshell):
>>
>> Thanks, Topi, I'll find time this week to look this over in detail.
>>
>> How much chattier does this make the syslog/journald during a regular
>> boot?  I was thinking "this is audit, we can choose what messages
>> will show up", but I guess that' sonly what auditd actually listens to,
>> not what kernel emits?  (sorry i've not looked at audit in a long
>> time).  Drat, that makes it seem like tracepoints would be better
>> after all.  But let's see how much it addes to the noise.
> 
> For example "loadkeys" causes thousands of entries. :-( I'm checking how
> to avoid audit message rate limiting, now some messages are lost.
> 
> It's still too easy to drown the logs with noise. That could be limited
> a lot by emitting a message only when the capability is used for the
> first time. But the question is how to define where to start counting
> (fork, exec, and/or setpcap?). I'm also not sure if that is the right
> way to log, since the first use of a capability could be expected and an
> innocent one, but then the 100th one could be malicious.
> 
> It's also very complex and error-prone to collect a capability mask from
> audit logs, which was my original goal.

What if only a summary of capabilities was logged at task exit? That
should make the log volume reasonable.

-Topi

> 
> -Topi
> 
>>
>>> BusyBox v1.22.1 (Debian 1:1.22.0-19) built-in shell (ash)
>>> Enter 'help' for a list of built-in commands.
>>>
>>> (initramfs) cd /sys/fs
>>> (initramfs) mount -t cgroup2 cgroup cgroup
>>> [   12.343152] audit_printk_skb: 5886 callbacks suppressed
>>> [   12.355214] audit: type=1300 audit(1468234317.100:518): arch=c000003e syscall=165 success=yes exit=0 a0=7fffe1e9ae2d a1=7fffe1e9ae34 a2=7fffe1e9ae25 a3=8000 items=0 ppid=469 pid=470 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mount" exe="/bin/mount" key=(null)
>>> [   12.414853] audit: type=1327 audit(1468234317.100:518): proctitle=6D6F756E74002D74006367726F757032006367726F7570006367726F7570
>>> [   12.438338] audit: type=1330 audit(1468234317.100:518): cap_used=0000000000200000
>>> [   12.453893] audit: type=1331 audit(1468234317.100:518): cgroups=:/;
>>> (initramfs) cd cgroup
>>> (initramfs) mkdir test; cd test
>>> [   17.335625] audit: type=1300 audit(1468234322.092:519): arch=c000003e syscall=83 success=yes exit=0 a0=7ffddfd75e29 a1=1ff a2=0 a3=1e2 items=0 ppid=469 pid=471 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mkdir" exe="/bin/mkdir" key=(null)
>>> [   17.392686] audit: type=1327 audit(1468234322.092:519): proctitle=6D6B6469720074657374
>>> [   17.409404] audit: type=1330 audit(1468234322.092:519): cap_used=0000000000000002
>>> [   17.425404] audit: type=1331 audit(1468234322.092:519): cgroups=:/;
>>> (initramfs) echo $$ >cgroup.procs
>>> (initramfs) mknod /dev/z_$$ c 1 2
>>> [   28.385681] audit: type=1300 audit(1468234333.144:520): arch=c000003e syscall=133 success=yes exit=0 a0=7ffe16324e11 a1=21b6 a2=102 a3=5c9 items=0 ppid=469 pid=472 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="mknod" exe="/bin/mknod" key=(null)
>>> [   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
>>> [   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
>>> [   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;
>>> (initramfs) chown 1234 /dev/z_*
>>> [   34.772992] audit: type=1300 audit(1468234339.532:521): arch=c000003e syscall=92 success=yes exit=0 a0=7ffd0b563e17 a1=4d2 a2=0 a3=60a items=0 ppid=469 pid=473 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=ttyS0 ses=4294967295 comm="chown" exe="/bin/chown" key=(null)
>>> [   34.828569] audit: type=1327 audit(1468234339.532:521): proctitle=63686F776E0031323334002F6465762F7A5F343639
>>> [   34.848747] audit: type=1330 audit(1468234339.532:521): cap_used=0000000000000001
>>> [   34.864404] audit: type=1331 audit(1468234339.532:521): cgroups=:/test;
>>>
>>> Signed-off-by: Topi Miettinen <toiwoton@gmail.com>
>>> ---
>>>  include/linux/audit.h      |  4 +++
>>>  include/linux/cgroup.h     |  2 ++
>>>  include/uapi/linux/audit.h |  2 ++
>>>  kernel/audit.c             |  7 +++---
>>>  kernel/audit.h             |  1 +
>>>  kernel/auditsc.c           | 28 ++++++++++++++++++++-
>>>  kernel/capability.c        |  5 ++--
>>>  kernel/cgroup.c            | 62 ++++++++++++++++++++++++++++++++++++++++++++++
>>>  8 files changed, 105 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/include/linux/audit.h b/include/linux/audit.h
>>> index e38e3fc..971cb2e 100644
>>> --- a/include/linux/audit.h
>>> +++ b/include/linux/audit.h
>>> @@ -438,6 +438,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>>>  		__audit_mmap_fd(fd, flags);
>>>  }
>>>  
>>> +extern void audit_log_cap_use(int cap);
>>> +
>>>  extern int audit_n_rules;
>>>  extern int audit_signals;
>>>  #else /* CONFIG_AUDITSYSCALL */
>>> @@ -545,6 +547,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>>>  { }
>>>  static inline void audit_ptrace(struct task_struct *t)
>>>  { }
>>> +static inline void audit_log_cap_use(int cap)
>>> +{ }
>>>  #define audit_n_rules 0
>>>  #define audit_signals 0
>>>  #endif /* CONFIG_AUDITSYSCALL */
>>> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
>>> index a20320c..b5dc8aa 100644
>>> --- a/include/linux/cgroup.h
>>> +++ b/include/linux/cgroup.h
>>> @@ -100,6 +100,8 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
>>>  int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
>>>  int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
>>>  		     struct pid *pid, struct task_struct *tsk);
>>> +struct audit_buffer;
>>> +void audit_cgroup_list(struct audit_buffer *ab);
>>>  
>>>  void cgroup_fork(struct task_struct *p);
>>>  extern int cgroup_can_fork(struct task_struct *p);
>>> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
>>> index d820aa9..c1ae016 100644
>>> --- a/include/uapi/linux/audit.h
>>> +++ b/include/uapi/linux/audit.h
>>> @@ -111,6 +111,8 @@
>>>  #define AUDIT_PROCTITLE		1327	/* Proctitle emit event */
>>>  #define AUDIT_FEATURE_CHANGE	1328	/* audit log listing feature changes */
>>>  #define AUDIT_REPLACE		1329	/* Replace auditd if this packet unanswerd */
>>> +#define AUDIT_CAPABILITY	1330	/* Record showing capability use */
>>> +#define AUDIT_CGROUP		1331	/* Record showing cgroups */
>>>  
>>>  #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
>>>  #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
>>> diff --git a/kernel/audit.c b/kernel/audit.c
>>> index 8d528f9..98dd920 100644
>>> --- a/kernel/audit.c
>>> +++ b/kernel/audit.c
>>> @@ -54,6 +54,7 @@
>>>  #include <linux/kthread.h>
>>>  #include <linux/kernel.h>
>>>  #include <linux/syscalls.h>
>>> +#include <linux/cgroup.h>
>>>  
>>>  #include <linux/audit.h>
>>>  
>>> @@ -1682,7 +1683,7 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
>>>  {
>>>  	int i;
>>>  
>>> -	audit_log_format(ab, " %s=", prefix);
>>> +	audit_log_format(ab, "%s=", prefix);
>>>  	CAP_FOR_EACH_U32(i) {
>>>  		audit_log_format(ab, "%08x",
>>>  				 cap->cap[CAP_LAST_U32 - i]);
>>> @@ -1696,11 +1697,11 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
>>>  	int log = 0;
>>>  
>>>  	if (!cap_isclear(*perm)) {
>>> -		audit_log_cap(ab, "cap_fp", perm);
>>> +		audit_log_cap(ab, " cap_fp", perm);
>>>  		log = 1;
>>>  	}
>>>  	if (!cap_isclear(*inh)) {
>>> -		audit_log_cap(ab, "cap_fi", inh);
>>> +		audit_log_cap(ab, " cap_fi", inh);
>>>  		log = 1;
>>>  	}
>>>  
>>> diff --git a/kernel/audit.h b/kernel/audit.h
>>> index a492f4c..680e8b5 100644
>>> --- a/kernel/audit.h
>>> +++ b/kernel/audit.h
>>> @@ -202,6 +202,7 @@ struct audit_context {
>>>  	};
>>>  	int fds[2];
>>>  	struct audit_proctitle proctitle;
>>> +	kernel_cap_t cap_used;
>>>  };
>>>  
>>>  extern u32 audit_ever_enabled;
>>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
>>> index 2672d10..32c3813 100644
>>> --- a/kernel/auditsc.c
>>> +++ b/kernel/auditsc.c
>>> @@ -197,7 +197,6 @@ static int audit_match_filetype(struct audit_context *ctx, int val)
>>>   * References in it _are_ dropped - at the same time we free/drop aux stuff.
>>>   */
>>>  
>>> -#ifdef CONFIG_AUDIT_TREE
>>>  static void audit_set_auditable(struct audit_context *ctx)
>>>  {
>>>  	if (!ctx->prio) {
>>> @@ -206,6 +205,7 @@ static void audit_set_auditable(struct audit_context *ctx)
>>>  	}
>>>  }
>>>  
>>> +#ifdef CONFIG_AUDIT_TREE
>>>  static int put_tree_ref(struct audit_context *ctx, struct audit_chunk *chunk)
>>>  {
>>>  	struct audit_tree_refs *p = ctx->trees;
>>> @@ -1439,6 +1439,18 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
>>>  
>>>  	audit_log_proctitle(tsk, context);
>>>  
>>> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
>>> +	if (ab) {
>>> +		audit_log_cap(ab, "cap_used", &context->cap_used);
>>> +		audit_log_end(ab);
>>> +	}
>>> +	ab = audit_log_start(context, GFP_KERNEL, AUDIT_CGROUP);
>>> +	if (ab) {
>>> +		audit_log_format(ab, "cgroups=");
>>> +		audit_cgroup_list(ab);
>>> +		audit_log_end(ab);
>>> +	}
>>> +
>>>  	/* Send end of event record to help user space know we are finished */
>>>  	ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
>>>  	if (ab)
>>> @@ -2428,3 +2440,17 @@ struct list_head *audit_killed_trees(void)
>>>  		return NULL;
>>>  	return &ctx->killed_trees;
>>>  }
>>> +
>>> +void audit_log_cap_use(int cap)
>>> +{
>>> +	struct audit_context *context = current->audit_context;
>>> +
>>> +	if (context) {
>>> +		cap_raise(context->cap_used, cap);
>>> +		audit_set_auditable(context);
>>> +	} else {
>>> +		audit_log(NULL, GFP_NOFS, AUDIT_CAPABILITY,
>>> +			  "cap_used=%d pid=%d no audit_context",
>>> +			  cap, task_pid_nr(current));
>>> +	}
>>> +}
>>> diff --git a/kernel/capability.c b/kernel/capability.c
>>> index 45432b5..d45d5b1 100644
>>> --- a/kernel/capability.c
>>> +++ b/kernel/capability.c
>>> @@ -366,8 +366,8 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
>>>   * @ns:  The usernamespace we want the capability in
>>>   * @cap: The capability to be tested for
>>>   *
>>> - * Return true if the current task has the given superior capability currently
>>> - * available for use, false if not.
>>> + * Return true if the current task has the given superior capability
>>> + * currently available for use, false if not. Write an audit message.
>>>   *
>>>   * This sets PF_SUPERPRIV on the task if the capability is available on the
>>>   * assumption that it's about to be used.
>>> @@ -380,6 +380,7 @@ bool ns_capable(struct user_namespace *ns, int cap)
>>>  	}
>>>  
>>>  	if (security_capable(current_cred(), ns, cap) == 0) {
>>> +		audit_log_cap_use(cap);
>>>  		current->flags |= PF_SUPERPRIV;
>>>  		return true;
>>>  	}
>>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>>> index 75c0ff0..1931679 100644
>>> --- a/kernel/cgroup.c
>>> +++ b/kernel/cgroup.c
>>> @@ -63,6 +63,7 @@
>>>  #include <linux/nsproxy.h>
>>>  #include <linux/proc_ns.h>
>>>  #include <net/sock.h>
>>> +#include <linux/audit.h>
>>>  
>>>  /*
>>>   * pidlists linger the following amount before being destroyed.  The goal
>>> @@ -5789,6 +5790,67 @@ out:
>>>  	return retval;
>>>  }
>>>  
>>> +/*
>>> + * audit_cgroup_list()
>>> + *  - Print task's cgroup paths with audit_log_format()
>>> + *  - Used for capability audit logging
>>> + *  - Otherwise very similar to proc_cgroup_show().
>>> + */
>>> +void audit_cgroup_list(struct audit_buffer *ab)
>>> +{
>>> +	char *buf, *path;
>>> +	struct cgroup_root *root;
>>> +
>>> +	buf = kmalloc(PATH_MAX, GFP_NOFS);
>>> +	if (!buf)
>>> +		return;
>>> +
>>> +	mutex_lock(&cgroup_mutex);
>>> +	spin_lock_irq(&css_set_lock);
>>> +
>>> +	for_each_root(root) {
>>> +		struct cgroup_subsys *ss;
>>> +		struct cgroup *cgrp;
>>> +		int ssid, count = 0;
>>> +
>>> +		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
>>> +			continue;
>>> +
>>> +		if (root != &cgrp_dfl_root)
>>> +			for_each_subsys(ss, ssid)
>>> +				if (root->subsys_mask & (1 << ssid))
>>> +					audit_log_format(ab, "%s%s",
>>> +							 count++ ? "," : "",
>>> +							 ss->legacy_name);
>>> +		if (strlen(root->name))
>>> +			audit_log_format(ab, "%sname=%s", count ? "," : "",
>>> +					 root->name);
>>> +		audit_log_format(ab, ":");
>>> +
>>> +		cgrp = task_cgroup_from_root(current, root);
>>> +
>>> +		if (cgroup_on_dfl(cgrp) || !(current->flags & PF_EXITING)) {
>>> +			path = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
>>> +						current->nsproxy->cgroup_ns);
>>> +			if (!path)
>>> +				goto out_unlock;
>>> +		} else
>>> +			path = "/";
>>> +
>>> +		audit_log_format(ab, "%s", path);
>>> +
>>> +		if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
>>> +			audit_log_format(ab, " (deleted);");
>>> +		else
>>> +			audit_log_format(ab, ";");
>>> +	}
>>> +
>>> +out_unlock:
>>> +	spin_unlock_irq(&css_set_lock);
>>> +	mutex_unlock(&cgroup_mutex);
>>> +	kfree(buf);
>>> +}
>>> +
>>>  /* Display information about each subsystem and each hierarchy */
>>>  static int proc_cgroupstats_show(struct seq_file *m, void *v)
>>>  {
>>> -- 
>>> 2.8.1
> 

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/11/16 17:09, Tejun Heo wrote:
> Hello,
> 
> On Mon, Jul 11, 2016 at 02:14:31PM +0300, Topi Miettinen wrote:
>> [   28.443674] audit: type=1327 audit(1468234333.144:520): proctitle=6D6B6E6F64002F6465762F7A5F343639006300310032
>> [   28.465888] audit: type=1330 audit(1468234333.144:520): cap_used=0000000008000000
>> [   28.482080] audit: type=1331 audit(1468234333.144:520): cgroups=:/test;
> 
> Please don't put additions of the two different audit types into one
> patch and I don't think the cgroup audit logging makes much sense.
> Without logging all migrations, it doesn't help auditing all that
> much.  Also, printing all cgroup membership like that can be
> problematic for audit it can be arbitrarily long.
> 
> Thanks.
> 

It's really critical to be able to associate a task in the logs to
cgroups which were valid that time. Or can we infer somehow what cgroups
a task was taking part, long time after task exit? Perhaps task cgroup
membership changes and changes in available cgroups should be logged too?

Some kind of cgroup IDs could be logged instead of long paths. Then
these IDs should be reliably resolvable to paths offline somehow.

How usual migrations between cgroups are? Why would a task ever move
from (say) systemd/system.slice/smartd.service to anywhere else?

-Topi

Re: [PATCH] capabilities: audit capability use

[Eric W. Biederman]

Topi Miettinen <toiwoton@gmail.com> writes:

> There are many basic ways to control processes, including capabilities,
> cgroups and resource limits. However, there are far fewer ways to find
> out useful values for the limits, except blind trial and error.
>
> Currently, there is no way to know which capabilities are actually used.
> Even the source code is only implicit, in-depth knowledge of each
> capability must be used when analyzing a program to judge which
> capabilities the program will exercise.
>
> Generate an audit message at system call exit, when capabilities are used.
> This can then be used to configure capability sets for services by a
> software developer, maintainer or system administrator.
>
> Test case demonstrating basic capability monitoring with the new
> message types 1330 and 1331 and how the cgroups are displayed (boot to
> rdshell):

You totally miss the interactions with the user namespace so this won't
give you the information you are aiming for.

Eric

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/11/16 21:57, Eric W. Biederman wrote:
> Topi Miettinen <toiwoton@gmail.com> writes:
> 
>> There are many basic ways to control processes, including capabilities,
>> cgroups and resource limits. However, there are far fewer ways to find
>> out useful values for the limits, except blind trial and error.
>>
>> Currently, there is no way to know which capabilities are actually used.
>> Even the source code is only implicit, in-depth knowledge of each
>> capability must be used when analyzing a program to judge which
>> capabilities the program will exercise.
>>
>> Generate an audit message at system call exit, when capabilities are used.
>> This can then be used to configure capability sets for services by a
>> software developer, maintainer or system administrator.
>>
>> Test case demonstrating basic capability monitoring with the new
>> message types 1330 and 1331 and how the cgroups are displayed (boot to
>> rdshell):
> 
> You totally miss the interactions with the user namespace so this won't
> give you the information you are aiming for.

Please correct me if this is not right:

There are two cases:
a) real capability use as seen outside the namespace
b) use of capabilities granted by the namespace
Both cases could be active independently.

For auditing purposes, we're  mostly interested in a) and log noise from
b) could be even seen a distraction.

For configuration purposes, both cases can be interesting, a) for the
configuration of  services and b) in case where the containerized
configuration is planned to be deployed outside. I'd still only log a).

The same logic should apply with cgroup namespaces.

-Topi

> 
> Eric
> 

Re: [PATCH] capabilities: audit capability use

[Eric W. Biederman]

Topi Miettinen <toiwoton@gmail.com> writes:

> On 07/11/16 21:57, Eric W. Biederman wrote:
>> Topi Miettinen <toiwoton@gmail.com> writes:
>> 
>>> There are many basic ways to control processes, including capabilities,
>>> cgroups and resource limits. However, there are far fewer ways to find
>>> out useful values for the limits, except blind trial and error.
>>>
>>> Currently, there is no way to know which capabilities are actually used.
>>> Even the source code is only implicit, in-depth knowledge of each
>>> capability must be used when analyzing a program to judge which
>>> capabilities the program will exercise.
>>>
>>> Generate an audit message at system call exit, when capabilities are used.
>>> This can then be used to configure capability sets for services by a
>>> software developer, maintainer or system administrator.
>>>
>>> Test case demonstrating basic capability monitoring with the new
>>> message types 1330 and 1331 and how the cgroups are displayed (boot to
>>> rdshell):
>> 
>> You totally miss the interactions with the user namespace so this won't
>> give you the information you are aiming for.
>
> Please correct me if this is not right:
>
> There are two cases:
> a) real capability use as seen outside the namespace
> b) use of capabilities granted by the namespace
> Both cases could be active independently.
>
> For auditing purposes, we're  mostly interested in a) and log noise from
> b) could be even seen a distraction.
>
> For configuration purposes, both cases can be interesting, a) for the
> configuration of  services and b) in case where the containerized
> configuration is planned to be deployed outside. I'd still only log
> a).
>
>
> The same logic should apply with cgroup namespaces.

Not logging capabilities outside of the initial user namespace is
certainly the conservative place to start, and what selinux does.

You should also be logging capability use from cap_capable.  Not
ns_capable.  You are missing several kinds of capability use as
a quick review of kernel/capability.c should have shown you.

Eric

Re: [PATCH] capabilities: audit capability use

[Tejun Heo]

On Mon, Jul 11, 2016 at 07:47:44PM +0000, Topi Miettinen wrote:
> It's really critical to be able to associate a task in the logs to
> cgroups which were valid that time. Or can we infer somehow what cgroups

When is "that time"?  Without logging all operations, this is
meaningless.

> a task was taking part, long time after task exit? Perhaps task cgroup
> membership changes and changes in available cgroups should be logged too?
> 
> Some kind of cgroup IDs could be logged instead of long paths. Then
> these IDs should be reliably resolvable to paths offline somehow.

I don't think that's doable.  That pretty much requires the kernel to
remember paths of all past cgroups.

> How usual migrations between cgroups are? Why would a task ever move
> from (say) systemd/system.slice/smartd.service to anywhere else?

In most cases, they won't move once set up initially but that's not
the point of audit subsystem.  Logging this once one exit isn't gonna
help anything for auditing the system.

Thanks.

-- 
tejun

Re: [PATCH] capabilities: audit capability use

[Paul Moore]

On Mon, Jul 11, 2016 at 7:14 AM, Topi Miettinen <toiwoton@gmail.com> wrote:
> There are many basic ways to control processes, including capabilities,
> cgroups and resource limits. However, there are far fewer ways to find
> out useful values for the limits, except blind trial and error.
>
> Currently, there is no way to know which capabilities are actually used.
> Even the source code is only implicit, in-depth knowledge of each
> capability must be used when analyzing a program to judge which
> capabilities the program will exercise.
>
> Generate an audit message at system call exit, when capabilities are used.
> This can then be used to configure capability sets for services by a
> software developer, maintainer or system administrator.
>
> Test case demonstrating basic capability monitoring with the new
> message types 1330 and 1331 and how the cgroups are displayed (boot to
> rdshell):

NOTE: additional comments inline with the patch.

I can understand the desire to audit the capabilities, but I'm a
little uncertain about the value of auditing cgroups at this point in
time.  The audit subsystem focuses primarily on security relevant
information, and while you could make an argument for cgroups here, I
think it is a relatively weak argument at the moment.

Also, please continue to work on reducing the impact of this on the
audit logs (your discussion with Serge).

> diff --git a/include/linux/audit.h b/include/linux/audit.h
> index e38e3fc..971cb2e 100644
> --- a/include/linux/audit.h
> +++ b/include/linux/audit.h
> @@ -438,6 +438,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>                 __audit_mmap_fd(fd, flags);
>  }
>
> +extern void audit_log_cap_use(int cap);
> +
>  extern int audit_n_rules;
>  extern int audit_signals;
>  #else /* CONFIG_AUDITSYSCALL */
> @@ -545,6 +547,8 @@ static inline void audit_mmap_fd(int fd, int flags)
>  { }
>  static inline void audit_ptrace(struct task_struct *t)
>  { }
> +static inline void audit_log_cap_use(int cap)
> +{ }
>  #define audit_n_rules 0
>  #define audit_signals 0
>  #endif /* CONFIG_AUDITSYSCALL */
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index a20320c..b5dc8aa 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -100,6 +100,8 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
>  int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
>  int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
>                      struct pid *pid, struct task_struct *tsk);
> +struct audit_buffer;
> +void audit_cgroup_list(struct audit_buffer *ab);
>
>  void cgroup_fork(struct task_struct *p);
>  extern int cgroup_can_fork(struct task_struct *p);
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index d820aa9..c1ae016 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -111,6 +111,8 @@
>  #define AUDIT_PROCTITLE                1327    /* Proctitle emit event */
>  #define AUDIT_FEATURE_CHANGE   1328    /* audit log listing feature changes */
>  #define AUDIT_REPLACE          1329    /* Replace auditd if this packet unanswerd */
> +#define AUDIT_CAPABILITY       1330    /* Record showing capability use */
> +#define AUDIT_CGROUP           1331    /* Record showing cgroups */

As Tejun Heo already stated, please put the capability changes and the
cgroup changes into two separate patches in one patchset.

>  #define AUDIT_AVC              1400    /* SE Linux avc denial or grant */
>  #define AUDIT_SELINUX_ERR      1401    /* Internal SE Linux Errors */
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 8d528f9..98dd920 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -54,6 +54,7 @@
>  #include <linux/kthread.h>
>  #include <linux/kernel.h>
>  #include <linux/syscalls.h>
> +#include <linux/cgroup.h>
>
>  #include <linux/audit.h>
>
> @@ -1682,7 +1683,7 @@ void audit_log_cap(struct audit_buffer *ab, char *prefix, kernel_cap_t *cap)
>  {
>         int i;
>
> -       audit_log_format(ab, " %s=", prefix);
> +       audit_log_format(ab, "%s=", prefix);

Why?

>         CAP_FOR_EACH_U32(i) {
>                 audit_log_format(ab, "%08x",
>                                  cap->cap[CAP_LAST_U32 - i]);
> @@ -1696,11 +1697,11 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
>         int log = 0;
>
>         if (!cap_isclear(*perm)) {
> -               audit_log_cap(ab, "cap_fp", perm);
> +               audit_log_cap(ab, " cap_fp", perm);

This is not an improvement, please stick with the leading space in
audit_log_cap() so callers do not have to worry about formatting
issues like this.

> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 2672d10..32c3813 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1439,6 +1439,18 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
>
>         audit_log_proctitle(tsk, context);
>
> +       ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
> +       if (ab) {
> +               audit_log_cap(ab, "cap_used", &context->cap_used);
> +               audit_log_end(ab);
> +       }
> +       ab = audit_log_start(context, GFP_KERNEL, AUDIT_CGROUP);
> +       if (ab) {
> +               audit_log_format(ab, "cgroups=");
> +               audit_cgroup_list(ab);

Why not just move the "cgroups=" into audit_cgroup_list()?  Can you
ever think of a reason why you would need to record the cgroups
without the "cgroup=" field prefix?

> +               audit_log_end(ab);
> +       }
> +
>         /* Send end of event record to help user space know we are finished */
>         ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
>         if (ab)
> @@ -2428,3 +2440,17 @@ struct list_head *audit_killed_trees(void)
>                 return NULL;
>         return &ctx->killed_trees;
>  }
> +
> +void audit_log_cap_use(int cap)
> +{
> +       struct audit_context *context = current->audit_context;
> +
> +       if (context) {
> +               cap_raise(context->cap_used, cap);
> +               audit_set_auditable(context);
> +       } else {
> +               audit_log(NULL, GFP_NOFS, AUDIT_CAPABILITY,
> +                         "cap_used=%d pid=%d no audit_context",
> +                         cap, task_pid_nr(current));
> +       }
> +}

You can't log "no audit_context" in the audit record, all information
logged should follow the "<field>=<value>" format.

-- 
paul moore
www.paul-moore.com

Re: [PATCH] capabilities: audit capability use

[Paul Moore]

On Tue, Jul 12, 2016 at 9:16 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Not logging capabilities outside of the initial user namespace is
> certainly the conservative place to start, and what selinux does.

FYI, we added some basic userns capability smarts to SELinux in Linux 4.7.

  commit 8e4ff6f228e4722cac74db716e308d1da33d744f
  Author: Stephen Smalley <sds@tycho.nsa.gov>
  Date:   Fri Apr 8 13:52:00 2016 -0400

   selinux: distinguish non-init user namespace capability checks

   Distinguish capability checks against a target associated
   with the init user namespace versus capability checks against
   a target associated with a non-init user namespace by defining
   and using separate security classes for the latter.

   This is needed to support e.g. Chrome usage of user namespaces
   for the Chrome sandbox without needing to allow Chrome to also
   exercise capabilities on targets in the init user namespace.

   Suggested-by: Dan Walsh <dwalsh@redhat.com>
   Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
   Signed-off-by: Paul Moore <paul@paul-moore.com>

-- 
paul moore
www.paul-moore.com

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/12/16 14:59, Tejun Heo wrote:
> On Mon, Jul 11, 2016 at 07:47:44PM +0000, Topi Miettinen wrote:
>> It's really critical to be able to associate a task in the logs to
>> cgroups which were valid that time. Or can we infer somehow what cgroups
> 
> When is "that time"?  Without logging all operations, this is
> meaningless.
> 
>> a task was taking part, long time after task exit? Perhaps task cgroup
>> membership changes and changes in available cgroups should be logged too?
>>
>> Some kind of cgroup IDs could be logged instead of long paths. Then
>> these IDs should be reliably resolvable to paths offline somehow.
> 
> I don't think that's doable.  That pretty much requires the kernel to
> remember paths of all past cgroups.

That's a show stopper for audit approach for getting helpful information
for configuration. I'll try something different, probably cgroupstats.

-Topi

> 
>> How usual migrations between cgroups are? Why would a task ever move
>> from (say) systemd/system.slice/smartd.service to anywhere else?
> 
> In most cases, they won't move once set up initially but that's not
> the point of audit subsystem.  Logging this once one exit isn't gonna
> help anything for auditing the system.
> 
> Thanks.
> 

Re: [PATCH] capabilities: audit capability use

[Topi Miettinen]

On 07/12/16 13:16, Eric W. Biederman wrote:
> Topi Miettinen <toiwoton@gmail.com> writes:
> 
>> On 07/11/16 21:57, Eric W. Biederman wrote:
>>> Topi Miettinen <toiwoton@gmail.com> writes:
>>>
>>>> There are many basic ways to control processes, including capabilities,
>>>> cgroups and resource limits. However, there are far fewer ways to find
>>>> out useful values for the limits, except blind trial and error.
>>>>
>>>> Currently, there is no way to know which capabilities are actually used.
>>>> Even the source code is only implicit, in-depth knowledge of each
>>>> capability must be used when analyzing a program to judge which
>>>> capabilities the program will exercise.
>>>>
>>>> Generate an audit message at system call exit, when capabilities are used.
>>>> This can then be used to configure capability sets for services by a
>>>> software developer, maintainer or system administrator.
>>>>
>>>> Test case demonstrating basic capability monitoring with the new
>>>> message types 1330 and 1331 and how the cgroups are displayed (boot to
>>>> rdshell):
>>>
>>> You totally miss the interactions with the user namespace so this won't
>>> give you the information you are aiming for.
>>
>> Please correct me if this is not right:
>>
>> There are two cases:
>> a) real capability use as seen outside the namespace
>> b) use of capabilities granted by the namespace
>> Both cases could be active independently.
>>
>> For auditing purposes, we're  mostly interested in a) and log noise from
>> b) could be even seen a distraction.
>>
>> For configuration purposes, both cases can be interesting, a) for the
>> configuration of  services and b) in case where the containerized
>> configuration is planned to be deployed outside. I'd still only log
>> a).
>>
>>
>> The same logic should apply with cgroup namespaces.
> 
> Not logging capabilities outside of the initial user namespace is
> certainly the conservative place to start, and what selinux does.
> 
> You should also be logging capability use from cap_capable.  Not

But cap_capable is not called from apparmor aa_capable or selinux
selinux_capable, how about security_capable()?

> ns_capable.  You are missing several kinds of capability use as
> a quick review of kernel/capability.c should have shown you.

Right, sorry about that.

-Topi

> 
> Eric
> 

Re: [PATCH] capabilities: audit capability use

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2500 bytes --]

Hi,

[auto build test ERROR on cgroup/for-next]
[also build test ERROR on v4.7-rc5]
[cannot apply to next-20160701]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Topi-Miettinen/capabilities-audit-capability-use/20160703-231120
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
config: microblaze-mmu_defconfig (attached as .config)
compiler: microblaze-linux-gcc (GCC) 4.9.0
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=microblaze 

All errors (new ones prefixed by >>):

>> kernel/audit.c:1713:6: error: redefinition of 'audit_log_cap_use'
    void audit_log_cap_use(int cap)
         ^
   In file included from kernel/audit.c:59:0:
   include/linux/audit.h:574:20: note: previous definition of 'audit_log_cap_use' was here
    static inline void audit_log_cap_use(int cap)
                       ^
   kernel/audit.c: In function 'audit_log_cap_use':
>> kernel/audit.c:1730:2: error: implicit declaration of function 'audit_cgroup_list' [-Werror=implicit-function-declaration]
     audit_cgroup_list(ab);
     ^
   cc1: some warnings being treated as errors

vim +/audit_log_cap_use +1713 kernel/audit.c

  1707	
  1708		if (log)
  1709			audit_log_format(ab, " cap_fe=%d cap_fver=%x",
  1710					 name->fcap.fE, name->fcap_ver);
  1711	}
  1712	
> 1713	void audit_log_cap_use(int cap)
  1714	{
  1715		struct audit_context *context = current->audit_context;
  1716		struct audit_buffer *ab;
  1717		kuid_t uid;
  1718		kgid_t gid;
  1719	
  1720		ab = audit_log_start(context, GFP_KERNEL, AUDIT_CAPABILITY);
  1721		audit_log_format(ab, "cap_used=%d", cap);
  1722		current_uid_gid(&uid, &gid);
  1723		audit_log_format(ab, " pid=%d auid=%u uid=%u gid=%u ses=%u",
  1724				 task_pid_nr(current),
  1725				 from_kuid(&init_user_ns, audit_get_loginuid(current)),
  1726				 from_kuid(&init_user_ns, uid),
  1727				 from_kgid(&init_user_ns, gid),
  1728				 audit_get_sessionid(current));
  1729		audit_log_format(ab, " cgroups=");
> 1730		audit_cgroup_list(ab);
  1731		audit_log_end(ab);
  1732	}
  1733	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 12626 bytes --]