[PATCH 02/10] audit: Fix possible spurious -ENOSPC error

[Paul Moore]

On Tue, Jul 10, 2018 at 6:02 AM Jan Kara <jack at suse.cz> wrote:
> When an inode is tagged with a tree, tag_chunk() checks whether there is
> audit_tree_group mark attached to the inode and adds one if not. However
> nothing protects another tag_chunk() to add the mark between we've
> checked and try to add the fsnotify mark thus resulting in an error from
> fsnotify_add_mark() and consequently an ENOSPC error from tag_chunk().
>
> Fix the problem by holding mark_mutex over the whole check-insert code
> sequence.
>
> Signed-off-by: Jan Kara <jack at suse.cz>
> ---
>  kernel/audit_tree.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)

...

> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index 1c82eb6674c4..de8d344d91b1 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -342,25 +342,29 @@ static void untag_chunk(struct node *p)
>         spin_lock(&hash_lock);
>  }
>
> +/* Call with group->mark_mutex held, releases it */

Stuff like that always makes me nervous.  Could we defer releasing the
mutex to the caller, after create_chunk() returns?  It looks like
fsnotify_destroy_mark() allows a single level of nesting so it should
be okay, yes?

--
paul moore
www.paul-moore.com