[PATCH v2] audit: Report suspicious O_CREAT usage

[PATCH v2] audit: Report suspicious O_CREAT usage

[Kees Cook]

This renames the very specific audit_log_link_denied() to
audit_log_path_denied() and adds the AUDIT_* type as an argument. This
allows for the creation of the new AUDIT_ANOM_CREAT that can be used to
report the fifo/regular file creation restrictions that were introduced
in commit 30aba6656f61 ("namei: allow restricted O_CREAT of FIFOs and
regular files"). Additionally further clarifies the existing
"operations" strings.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v2:
 - fix build failure typo in CONFIG_AUDIT=n case
 - improve operations naming (paul)
---
 fs/namei.c                 |  8 ++++++--
 include/linux/audit.h      |  5 +++--
 include/uapi/linux/audit.h |  1 +
 kernel/audit.c             | 11 ++++++-----
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 671c3c1a3425..2d5d245ae723 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -925,7 +925,7 @@ static inline int may_follow_link(struct nameidata *nd)
 		return -ECHILD;
 
 	audit_inode(nd->name, nd->stack[0].link.dentry, 0);
-	audit_log_link_denied("follow_link");
+	audit_log_path_denied(AUDIT_ANOM_LINK, "sticky_follow_link");
 	return -EACCES;
 }
 
@@ -993,7 +993,7 @@ static int may_linkat(struct path *link)
 	if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
 		return 0;
 
-	audit_log_link_denied("linkat");
+	audit_log_path_denied(AUDIT_ANOM_LINK, "unowned_linkat");
 	return -EPERM;
 }
 
@@ -1031,6 +1031,10 @@ static int may_create_in_sticky(struct dentry * const dir,
 	    (dir->d_inode->i_mode & 0020 &&
 	     ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
 	      (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
+		const char *operation = S_ISFIFO(inode->i_mode) ?
+					"sticky_create_fifo" :
+					"sticky_create_regular";
+		audit_log_path_denied(AUDIT_ANOM_CREAT, operation);
 		return -EACCES;
 	}
 	return 0;
diff --git a/include/linux/audit.h b/include/linux/audit.h
index aee3dc9eb378..f9ceae57ca8d 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -156,7 +156,8 @@ extern void		    audit_log_d_path(struct audit_buffer *ab,
 					     const struct path *path);
 extern void		    audit_log_key(struct audit_buffer *ab,
 					  char *key);
-extern void		    audit_log_link_denied(const char *operation);
+extern void		    audit_log_path_denied(int type,
+						  const char *operation);
 extern void		    audit_log_lost(const char *message);
 
 extern int audit_log_task_context(struct audit_buffer *ab);
@@ -217,7 +218,7 @@ static inline void audit_log_d_path(struct audit_buffer *ab,
 { }
 static inline void audit_log_key(struct audit_buffer *ab, char *key)
 { }
-static inline void audit_log_link_denied(const char *string)
+static inline void audit_log_path_denied(int type, const char *operation)
 { }
 static inline int audit_log_task_context(struct audit_buffer *ab)
 {
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index c89c6495983d..3ad935527177 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -143,6 +143,7 @@
 #define AUDIT_ANOM_PROMISCUOUS      1700 /* Device changed promiscuous mode */
 #define AUDIT_ANOM_ABEND            1701 /* Process ended abnormally */
 #define AUDIT_ANOM_LINK		    1702 /* Suspicious use of file links */
+#define AUDIT_ANOM_CREAT	    1703 /* Suspicious file creation */
 #define AUDIT_INTEGRITY_DATA	    1800 /* Data integrity verification */
 #define AUDIT_INTEGRITY_METADATA    1801 /* Metadata integrity verification */
 #define AUDIT_INTEGRITY_STATUS	    1802 /* Integrity enable status */
diff --git a/kernel/audit.c b/kernel/audit.c
index da8dc0db5bd3..d75485aa25ff 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -2155,18 +2155,19 @@ void audit_log_task_info(struct audit_buffer *ab)
 EXPORT_SYMBOL(audit_log_task_info);
 
 /**
- * audit_log_link_denied - report a link restriction denial
- * @operation: specific link operation
+ * audit_log_path_denied - report a path restriction denial
+ * @type: audit message type (AUDIT_ANOM_LINK, AUDIT_ANOM_CREAT, etc)
+ * @operation: specific operation name
  */
-void audit_log_link_denied(const char *operation)
+void audit_log_path_denied(int type, const char *operation)
 {
 	struct audit_buffer *ab;
 
 	if (!audit_enabled || audit_dummy_context())
 		return;
 
-	/* Generate AUDIT_ANOM_LINK with subject, operation, outcome. */
-	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_ANOM_LINK);
+	/* Generate log with subject, operation, outcome. */
+	ab = audit_log_start(audit_context(), GFP_KERNEL, type);
 	if (!ab)
 		return;
 	audit_log_format(ab, "op=%s", operation);
-- 
2.17.1


-- 
Kees Cook

Re: [PATCH v2] audit: Report suspicious O_CREAT usage

[Paul Moore]

On Tue, Oct 1, 2019 at 12:48 PM Kees Cook <keescook@chromium.org> wrote:
>
> This renames the very specific audit_log_link_denied() to
> audit_log_path_denied() and adds the AUDIT_* type as an argument. This
> allows for the creation of the new AUDIT_ANOM_CREAT that can be used to
> report the fifo/regular file creation restrictions that were introduced
> in commit 30aba6656f61 ("namei: allow restricted O_CREAT of FIFOs and
> regular files"). Additionally further clarifies the existing
> "operations" strings.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2:
>  - fix build failure typo in CONFIG_AUDIT=n case
>  - improve operations naming (paul)
> ---
>  fs/namei.c                 |  8 ++++++--
>  include/linux/audit.h      |  5 +++--
>  include/uapi/linux/audit.h |  1 +
>  kernel/audit.c             | 11 ++++++-----
>  4 files changed, 16 insertions(+), 9 deletions(-)

Thanks for the update, but I think we need another respin, see below.

> diff --git a/fs/namei.c b/fs/namei.c
> index 671c3c1a3425..2d5d245ae723 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -925,7 +925,7 @@ static inline int may_follow_link(struct nameidata *nd)
>                 return -ECHILD;
>
>         audit_inode(nd->name, nd->stack[0].link.dentry, 0);
> -       audit_log_link_denied("follow_link");
> +       audit_log_path_denied(AUDIT_ANOM_LINK, "sticky_follow_link");

Maybe I should have been more clear in the last patch thread, but my
suggested name change was only for the new records you are adding; we
don't want to change the operation/op names for existing records.  In
the above change, "follow_link" should stay "follow_link".

> @@ -993,7 +993,7 @@ static int may_linkat(struct path *link)
>         if (safe_hardlink_source(inode) || inode_owner_or_capable(inode))
>                 return 0;
>
> -       audit_log_link_denied("linkat");
> +       audit_log_path_denied(AUDIT_ANOM_LINK, "unowned_linkat");

See above, this should stay as "linkat".

> @@ -1031,6 +1031,10 @@ static int may_create_in_sticky(struct dentry * const dir,
>             (dir->d_inode->i_mode & 0020 &&
>              ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
>               (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
> +               const char *operation = S_ISFIFO(inode->i_mode) ?
> +                                       "sticky_create_fifo" :
> +                                       "sticky_create_regular";
> +               audit_log_path_denied(AUDIT_ANOM_CREAT, operation);

This is a new record, so this is fine.  Thanks for changing this.

-- 
paul moore
www.paul-moore.com