[PATCH] ceph: check i_nlink while converting a file handle to dentry

From: Luis Henriques
Date: Wed May 17 2017 - 07:26:44 EST

Converting a file handle to a dentry can be done call after the inode
unlink. This means that __fh_to_dentry() requires an extra check to
verify the number of links is not 0.

The issue can be easily reproduced using xfstest generic/426, which does
something like:

echo 3 > /proc/sys/vm/drop_caches

The call to open_by_handle_at() should fail, as the file doesn't exist

Cc: stable@xxxxxxxxxxxxxxx
Link: http://tracker.ceph.com/issues/19958
Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx>
fs/ceph/export.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/fs/ceph/export.c b/fs/ceph/export.c
index e8f11fa565c5..7df550c13d7f 100644
--- a/fs/ceph/export.c
+++ b/fs/ceph/export.c
@@ -91,6 +91,10 @@ static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
if (!inode)
return ERR_PTR(-ESTALE);
+ if (inode->i_nlink == 0) {
+ iput(inode);
+ return ERR_PTR(-ESTALE);
+ }

return d_obtain_alias(inode);