[PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

[PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

[Jan Kara]

audit_remove_watch_rule() drops watch's reference to parent but then
continues to work with it. That is not safe as parent can get freed once
we drop our reference. The following is a trivial reproducer:

mount -o loop image /mnt
touch /mnt/file
auditctl -w /mnt/file -p wax
umount /mnt
auditctl -D
<crash in fsnotify_destroy_mark()>

Grab our own reference in audit_remove_watch_rule() earlier to make sure
mark does not get freed under us.

CC: stable@vger.kernel.org
Reported-by: Tony Jones <tonyj@suse.de>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 kernel/audit_watch.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index 62d686d96581..ed748ee40029 100644
--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -457,13 +457,15 @@ void audit_remove_watch_rule(struct audit_krule *krule)
 	list_del(&krule->rlist);
 
 	if (list_empty(&watch->rules)) {
+		/*
+		 * audit_remove_watch() drops our reference to 'parent' which
+		 * can get freed. Grab our own reference to be safe.
+		 */
+		audit_get_parent(parent);
 		audit_remove_watch(watch);
-
-		if (list_empty(&parent->watches)) {
-			audit_get_parent(parent);
+		if (list_empty(&parent->watches))
 			fsnotify_destroy_mark(&parent->mark, audit_watch_group);
-			audit_put_parent(parent);
-		}
+		audit_put_parent(parent);
 	}
 }
 
-- 
2.12.3

Re: [PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

[Tony Jones]

On 08/15/2017 04:00 AM, Jan Kara wrote:
> audit_remove_watch_rule() drops watch's reference to parent but then
> continues to work with it. That is not safe as parent can get freed once
> we drop our reference. The following is a trivial reproducer:
> 
> mount -o loop image /mnt
> touch /mnt/file
> auditctl -w /mnt/file -p wax
> umount /mnt
> auditctl -D
> <crash in fsnotify_destroy_mark()>
> 
> Grab our own reference in audit_remove_watch_rule() earlier to make sure
> mark does not get freed under us.
> 
> CC: stable@vger.kernel.org
> Reported-by: Tony Jones <tonyj@suse.de>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---

Tested-by: Tony Jones <tonyj@suse.de>

Fix tested and verified against v3.0 and mainline

Re: [PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

[Paul Moore]

On Tue, Aug 15, 2017 at 7:00 AM, Jan Kara <jack@suse.cz> wrote:
> audit_remove_watch_rule() drops watch's reference to parent but then
> continues to work with it. That is not safe as parent can get freed once
> we drop our reference. The following is a trivial reproducer:
>
> mount -o loop image /mnt
> touch /mnt/file
> auditctl -w /mnt/file -p wax
> umount /mnt
> auditctl -D
> <crash in fsnotify_destroy_mark()>
>
> Grab our own reference in audit_remove_watch_rule() earlier to make sure
> mark does not get freed under us.
>
> CC: stable@vger.kernel.org
> Reported-by: Tony Jones <tonyj@suse.de>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  kernel/audit_watch.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

This looks good to me, thanks for the fix.  I'm going to merge this
into the audit/stable-4.13 branch and assuming it passes the audit
tests I'll send it up to Linus later this week.

> diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
> index 62d686d96581..ed748ee40029 100644
> --- a/kernel/audit_watch.c
> +++ b/kernel/audit_watch.c
> @@ -457,13 +457,15 @@ void audit_remove_watch_rule(struct audit_krule *krule)
>         list_del(&krule->rlist);
>
>         if (list_empty(&watch->rules)) {
> +               /*
> +                * audit_remove_watch() drops our reference to 'parent' which
> +                * can get freed. Grab our own reference to be safe.
> +                */
> +               audit_get_parent(parent);
>                 audit_remove_watch(watch);
> -
> -               if (list_empty(&parent->watches)) {
> -                       audit_get_parent(parent);
> +               if (list_empty(&parent->watches))
>                         fsnotify_destroy_mark(&parent->mark, audit_watch_group);
> -                       audit_put_parent(parent);
> -               }
> +               audit_put_parent(parent);
>         }
>  }
>
> --
> 2.12.3

-- 
paul moore
www.paul-moore.com

Re: [PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

[Richard Guy Briggs]

On 2017-08-15 13:00, Jan Kara wrote:
> audit_remove_watch_rule() drops watch's reference to parent but then
> continues to work with it. That is not safe as parent can get freed once
> we drop our reference. The following is a trivial reproducer:
> 
> mount -o loop image /mnt
> touch /mnt/file
> auditctl -w /mnt/file -p wax
> umount /mnt
> auditctl -D
> <crash in fsnotify_destroy_mark()>
> 
> Grab our own reference in audit_remove_watch_rule() earlier to make sure
> mark does not get freed under us.
> 
> CC: stable@vger.kernel.org
> Reported-by: Tony Jones <tonyj@suse.de>
> Signed-off-by: Jan Kara <jack@suse.cz>

Reviewed-by: Richard Guy Briggs <rgb@redhat.com>

> ---
>  kernel/audit_watch.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
> index 62d686d96581..ed748ee40029 100644
> --- a/kernel/audit_watch.c
> +++ b/kernel/audit_watch.c
> @@ -457,13 +457,15 @@ void audit_remove_watch_rule(struct audit_krule *krule)
>  	list_del(&krule->rlist);
>  
>  	if (list_empty(&watch->rules)) {
> +		/*
> +		 * audit_remove_watch() drops our reference to 'parent' which
> +		 * can get freed. Grab our own reference to be safe.
> +		 */
> +		audit_get_parent(parent);
>  		audit_remove_watch(watch);
> -
> -		if (list_empty(&parent->watches)) {
> -			audit_get_parent(parent);
> +		if (list_empty(&parent->watches))
>  			fsnotify_destroy_mark(&parent->mark, audit_watch_group);
> -			audit_put_parent(parent);
> -		}
> +		audit_put_parent(parent);
>  	}
>  }
>  
> -- 
> 2.12.3
> 
> --
> Linux-audit mailing list
> Linux-audit@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-audit

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635