On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack@xxxxxxx> wrote:
> Audit tree code was happily adding new notification marks while holding
> spinlocks. Since fsnotify_add_mark() acquires group->mark_mutex this can
> lead to sleeping while holding a spinlock, deadlocks due to lock
> inversion, and probably other fun. Fix the problem by acquiring
> group->mark_mutex earlier.
>
> CC: Paul Moore <paul@xxxxxxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> kernel/audit_tree.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
[SIDE NOTE: this patch explains your comments and my earlier concern
about the locked/unlocked variants of fsnotify_add_mark() in
untag_chunk()]
Ouch. Thanks for catching this ... what is your goal with these
patches, are you targeting this as a fix during the v4.10-rcX cycle?
If not, any objections if I pull this patch into the audit tree and
send this to Linus during the v4.10-rcX cycle (assuming it passes
testing, yadda yadda)?
> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index f3130eb0a4bd..156b6a93f4fc 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -231,6 +231,7 @@ static void untag_chunk(struct node *p)
> if (size)
> new = alloc_chunk(size);
>
> + mutex_lock(&entry->group->mark_mutex);
> spin_lock(&entry->lock);
> if (chunk->dead || !entry->inode) {
> spin_unlock(&entry->lock);
> @@ -258,7 +259,8 @@ static void untag_chunk(struct node *p)
> if (!new)
> goto Fallback;
>
> - if (fsnotify_add_mark(&new->mark, entry->group, entry->inode, NULL, 1)) {
> + if (fsnotify_add_mark_locked(&new->mark, entry->group, entry->inode,
> + NULL, 1)) {
> fsnotify_put_mark(&new->mark);
> goto Fallback;
> }
> @@ -309,6 +311,7 @@ static void untag_chunk(struct node *p)
> spin_unlock(&hash_lock);
> spin_unlock(&entry->lock);
> out:
> + mutex_unlock(&entry->group->mark_mutex);
> fsnotify_put_mark(entry);
> spin_lock(&hash_lock);
> }
> @@ -385,17 +388,21 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
>
> chunk_entry = &chunk->mark;
>
> + mutex_lock(&old_entry->group->mark_mutex);
> spin_lock(&old_entry->lock);
> if (!old_entry->inode) {
> /* old_entry is being shot, lets just lie */
> spin_unlock(&old_entry->lock);
> + mutex_unlock(&old_entry->group->mark_mutex);
> fsnotify_put_mark(old_entry);
> free_chunk(chunk);
> return -ENOENT;
> }
>
> - if (fsnotify_add_mark(chunk_entry, old_entry->group, old_entry->inode, NULL, 1)) {
> + if (fsnotify_add_mark_locked(chunk_entry, old_entry->group,
> + old_entry->inode, NULL, 1)) {
> spin_unlock(&old_entry->lock);
> + mutex_unlock(&old_entry->group->mark_mutex);
> fsnotify_put_mark(chunk_entry);
> fsnotify_put_mark(old_entry);
> return -ENOSPC;
> @@ -411,6 +418,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> chunk->dead = 1;
> spin_unlock(&chunk_entry->lock);
> spin_unlock(&old_entry->lock);
> + mutex_unlock(&old_entry->group->mark_mutex);
>
> fsnotify_destroy_mark(chunk_entry, audit_tree_group);
>
> @@ -443,6 +451,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> spin_unlock(&hash_lock);
> spin_unlock(&chunk_entry->lock);
> spin_unlock(&old_entry->lock);
> + mutex_unlock(&old_entry->group->mark_mutex);
> fsnotify_destroy_mark(old_entry, audit_tree_group);
> fsnotify_put_mark(chunk_entry); /* drop initial reference */
> fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
> --
> 2.10.2
>
--
paul moore
www.paul-moore.com
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
