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* [PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps
@ 2014-10-19 18:05 Sebastian Schmidt
  2014-10-20 18:15 ` Kees Cook
  0 siblings, 1 reply; 2+ messages in thread
From: Sebastian Schmidt @ 2014-10-19 18:05 UTC (permalink / raw)
  To: Anton Vorontsov, Colin Cross, Kees Cook, Tony Luck; +Cc: linux-kernel

When the kernel.dmesg_restrict restriction is in place, only users with
CAP_SYSLOG should be able to access crash dumps (like: attacker is
trying to exploit a bug, watchdog reboots, attacker can happily read
crash dumps and logs).

This puts the restriction on console-* types as well as sensitive
information could have been leaked there.

Other log types are unaffected.

Signed-off-by: Sebastian Schmidt <yath@yath.de>
---
 fs/pstore/inode.c      | 22 ++++++++++++++++++++++
 include/linux/syslog.h |  1 +
 kernel/printk/printk.c |  2 +-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index fafb7a0..5041660 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -36,6 +36,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/uaccess.h>
+#include <linux/syslog.h>
 
 #include "internal.h"
 
@@ -120,6 +121,18 @@ static const struct seq_operations pstore_ftrace_seq_ops = {
 	.show	= pstore_ftrace_seq_show,
 };
 
+static int pstore_check_syslog_permissions(struct pstore_private *ps)
+{
+	switch (ps->type) {
+	case PSTORE_TYPE_DMESG:
+	case PSTORE_TYPE_CONSOLE:
+		return check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+			SYSLOG_FROM_READER);
+	default:
+		return 0;
+	}
+}
+
 static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
 						size_t count, loff_t *ppos)
 {
@@ -138,6 +151,10 @@ static int pstore_file_open(struct inode *inode, struct file *file)
 	int err;
 	const struct seq_operations *sops = NULL;
 
+	err = pstore_check_syslog_permissions(ps);
+	if (err)
+		return err;
+
 	if (ps->type == PSTORE_TYPE_FTRACE)
 		sops = &pstore_ftrace_seq_ops;
 
@@ -174,6 +191,11 @@ static const struct file_operations pstore_file_operations = {
 static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 {
 	struct pstore_private *p = dentry->d_inode->i_private;
+	int err;
+
+	err = pstore_check_syslog_permissions(p);
+	if (err)
+		return err;
 
 	if (p->psi->erase)
 		p->psi->erase(p->type, p->id, p->count,
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 98a3153..9def529 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -48,5 +48,6 @@
 #define SYSLOG_FROM_PROC             1
 
 int do_syslog(int type, char __user *buf, int count, bool from_file);
+int check_syslog_permissions(int type, bool from_file);
 
 #endif /* _LINUX_SYSLOG_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ced2b84..c8755e7 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -480,7 +480,7 @@ static int syslog_action_restricted(int type)
 	       type != SYSLOG_ACTION_SIZE_BUFFER;
 }
 
-static int check_syslog_permissions(int type, bool from_file)
+int check_syslog_permissions(int type, bool from_file)
 {
 	/*
 	 * If this is from /proc/kmsg and we've already opened it, then we've
-- 
2.1.1


^ permalink raw reply related	[flat|nested] 2+ messages in thread
* Re: [PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps
  2014-10-19 18:05 [PATCH] pstore: honor dmesg_restrict sysctl on dmesg dumps Sebastian Schmidt
@ 2014-10-20 18:15 ` Kees Cook
  0 siblings, 0 replies; 2+ messages in thread
From: Kees Cook @ 2014-10-20 18:15 UTC (permalink / raw)
  To: Sebastian Schmidt; +Cc: Anton Vorontsov, Colin Cross, Tony Luck, LKML

On Sun, Oct 19, 2014 at 11:05 AM, Sebastian Schmidt <yath@yath.de> wrote:
> When the kernel.dmesg_restrict restriction is in place, only users with
> CAP_SYSLOG should be able to access crash dumps (like: attacker is
> trying to exploit a bug, watchdog reboots, attacker can happily read
> crash dumps and logs).
>
> This puts the restriction on console-* types as well as sensitive
> information could have been leaked there.
>
> Other log types are unaffected.
>
> Signed-off-by: Sebastian Schmidt <yath@yath.de>

This looks sensible to me; thanks!

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  fs/pstore/inode.c      | 22 ++++++++++++++++++++++
>  include/linux/syslog.h |  1 +
>  kernel/printk/printk.c |  2 +-
>  3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
> index fafb7a0..5041660 100644
> --- a/fs/pstore/inode.c
> +++ b/fs/pstore/inode.c
> @@ -36,6 +36,7 @@
>  #include <linux/slab.h>
>  #include <linux/spinlock.h>
>  #include <linux/uaccess.h>
> +#include <linux/syslog.h>
>
>  #include "internal.h"
>
> @@ -120,6 +121,18 @@ static const struct seq_operations pstore_ftrace_seq_ops = {
>         .show   = pstore_ftrace_seq_show,
>  };
>
> +static int pstore_check_syslog_permissions(struct pstore_private *ps)
> +{
> +       switch (ps->type) {
> +       case PSTORE_TYPE_DMESG:
> +       case PSTORE_TYPE_CONSOLE:
> +               return check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
> +                       SYSLOG_FROM_READER);
> +       default:
> +               return 0;
> +       }
> +}
> +
>  static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
>                                                 size_t count, loff_t *ppos)
>  {
> @@ -138,6 +151,10 @@ static int pstore_file_open(struct inode *inode, struct file *file)
>         int err;
>         const struct seq_operations *sops = NULL;
>
> +       err = pstore_check_syslog_permissions(ps);
> +       if (err)
> +               return err;
> +
>         if (ps->type == PSTORE_TYPE_FTRACE)
>                 sops = &pstore_ftrace_seq_ops;
>
> @@ -174,6 +191,11 @@ static const struct file_operations pstore_file_operations = {
>  static int pstore_unlink(struct inode *dir, struct dentry *dentry)
>  {
>         struct pstore_private *p = dentry->d_inode->i_private;
> +       int err;
> +
> +       err = pstore_check_syslog_permissions(p);
> +       if (err)
> +               return err;
>
>         if (p->psi->erase)
>                 p->psi->erase(p->type, p->id, p->count,
> diff --git a/include/linux/syslog.h b/include/linux/syslog.h
> index 98a3153..9def529 100644
> --- a/include/linux/syslog.h
> +++ b/include/linux/syslog.h
> @@ -48,5 +48,6 @@
>  #define SYSLOG_FROM_PROC             1
>
>  int do_syslog(int type, char __user *buf, int count, bool from_file);
> +int check_syslog_permissions(int type, bool from_file);
>
>  #endif /* _LINUX_SYSLOG_H */
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index ced2b84..c8755e7 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -480,7 +480,7 @@ static int syslog_action_restricted(int type)
>                type != SYSLOG_ACTION_SIZE_BUFFER;
>  }
>
> -static int check_syslog_permissions(int type, bool from_file)
> +int check_syslog_permissions(int type, bool from_file)
>  {
>         /*
>          * If this is from /proc/kmsg and we've already opened it, then we've
> --
> 2.1.1
>



-- 
Kees Cook
Chrome OS Security

^ permalink raw reply	[flat|nested] 2+ messages in thread
end of thread, other threads:[~2014-10-20 18:16 UTC | newest]

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