| From | Ben Hutchings <> | Date | Sun, 09 Dec 2018 21:50:33 +0000 | Subject | [PATCH 3.16 317/328] cachefiles: fix the race between cachefiles_bury_object() and rmdir(2) |
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3.16.62-rc1 review patch. If anyone has any objections, please let me know.
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From: Al Viro <viro@zeniv.linux.org.uk>
commit 169b803397499be85bdd1e3d07d6f5e3d4bd669e upstream.
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.
Fixes: 9ae326a69004 (CacheFiles: A cache that backs onto a mounted filesystem) Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- fs/cachefiles/namei.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/cachefiles/namei.c +++ b/fs/cachefiles/namei.c @@ -317,7 +317,7 @@ try_again: 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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