[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 at vger.kernel.org
> Reported-by: Tony Jones <tonyj at suse.de>
> Signed-off-by: Jan Kara <jack at suse.cz>

Reviewed-by: Richard Guy Briggs <rgb at 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
> 
> --
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- RGB

--
Richard Guy Briggs <rgb at 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