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Message-ID: <153978582166.7579.12678499150203462777.stgit@warthog.procyon.org.uk>
Date: Wed, 17 Oct 2018 15:17:01 +0100
From: David Howells <dhowells@...hat.com>
To: gregkh@...ux-foundation.org
Cc: stable@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
viro@...iv.linux.org.uk, sandeen@...hat.com, dhowells@...hat.com,
linux-cachefs@...hat.com, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] cachefiles: fix the race between
cachefiles_bury_object() and rmdir(2)
From: Al Viro <viro@...iv.linux.org.uk>
the victim might've been rmdir'ed just before the lock_rename();
unlike the normal callers, we do not look the source up after the
parents are locked - we know it beforehand and just recheck that it's
still the child of what used to be its parent. Unfortunately,
the check is too weak - we don't spot a dead directory since its
->d_parent is unchanged, dentry is positive, etc. So we sail all
the way to ->rename(), with hosting filesystems _not_ expecting
to be asked renaming an rmdir'ed subdirectory.
The fix is easy, fortunately - the lock on parent is sufficient for
making IS_DEADDIR() on child safe.
Cc: stable@...r.kernel.org
Fixes: 9ae326a69004 (CacheFiles: A cache that backs onto a mounted filesystem)
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: David Howells <dhowells@...hat.com>
---
fs/cachefiles/namei.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index af2b17b21b94..95983c744164 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -343,7 +343,7 @@ static int cachefiles_bury_object(struct cachefiles_cache *cache,
trap = lock_rename(cache->graveyard, dir);
/* do some checks before getting the grave dentry */
- if (rep->d_parent != dir) {
+ if (rep->d_parent != dir || IS_DEADDIR(d_inode(rep))) {
/* the entry was probably culled when we dropped the parent dir
* lock */
unlock_rename(cache->graveyard, dir);
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