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inotify: race use after free/double free in inotify inode marks

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There is a race in the inotify add/rm watch code.  A task can find and
remove a mark which doesn't have all of it's references.  This can
result in a use after free/double free situation.

Task A					Task B
------------				-----------
inotify_new_watch()
 allocate a mark (refcnt == 1)
 add it to the idr
					inotify_rm_watch()
					 inotify_remove_from_idr()
					  fsnotify_put_mark()
					      refcnt hits 0, free
 take reference because we are on idr
 [at this point it is a use after free]
 [time goes on]
 refcnt may hit 0 again, double free

The fix is to take the reference BEFORE the object can be found in the
idr.

Signed-off-by: Eric Paris <eparis@redhat.com>
Cc: <stable@kernel.org>
This commit is contained in:
Eric Paris 2010-05-11 17:17:40 -04:00
parent 3dbc6fb6a3
commit e08733446e
1 changed files with 6 additions and 3 deletions
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9
fs/notify/inotify/inotify_user.c
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@ -546,21 +546,24 @@ static int inotify_new_watch(struct fsnotify_group *group,
if (unlikely(!idr_pre_get(&group->inotify_data.idr, GFP_KERNEL)))
goto out_err;
/* we are putting the mark on the idr, take a reference */
fsnotify_get_mark(&tmp_ientry->fsn_entry);
spin_lock(&group->inotify_data.idr_lock);
ret = idr_get_new_above(&group->inotify_data.idr, &tmp_ientry->fsn_entry,
group->inotify_data.last_wd+1,
&tmp_ientry->wd);
spin_unlock(&group->inotify_data.idr_lock);
if (ret) {
/* we didn't get on the idr, drop the idr reference */
fsnotify_put_mark(&tmp_ientry->fsn_entry);
/* idr was out of memory allocate and try again */
if (ret == -EAGAIN)
goto retry;
goto out_err;
}
/* we put the mark on the idr, take a reference */
fsnotify_get_mark(&tmp_ientry->fsn_entry);
/* we are on the idr, now get on the inode */
ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode);
if (ret) {