[PATCH 4.19 014/243] exportfs_decode_fh(): negative pinned may become positive without the parent locked

Greg Kroah-Hartman
2019-12-11T15:16:16Z

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit a2ece088882666e1dc7113744ac912eb161e3f87 ]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/exportfs/expfs.c | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 63707abcbeb3e..808cae6d5f50f 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -517,26 +517,33 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
* inode is actually connected to the parent.
*/
err = exportfs_get_name(mnt, target_dir, nbuf, result);
- if (!err) {
- inode_lock(target_dir->d_inode);
- nresult = lookup_one_len(nbuf, target_dir,
- strlen(nbuf));
- inode_unlock(target_dir->d_inode);
- if (!IS_ERR(nresult)) {
- if (nresult->d_inode) {
- dput(result);
- result = nresult;
- } else
- dput(nresult);
- }
+ if (err) {
+ dput(target_dir);
+ goto err_result;
}

+ inode_lock(target_dir->d_inode);
+ nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
+ if (!IS_ERR(nresult)) {
+ if (unlikely(nresult->d_inode != result->d_inode)) {
+ dput(nresult);
+ nresult = ERR_PTR(-ESTALE);
+ }
+ }
+ inode_unlock(target_dir->d_inode);
/*
* At this point we are done with the parent, but it's pinned
* by the child dentry anyway.
*/
dput(target_dir);

+ if (IS_ERR(nresult)) {
+ err = PTR_ERR(nresult);
+ goto err_result;
+ }
+ dput(result);
+ result = nresult;
+
/*
* And finally make sure the dentry is actually acceptable
* to NFSD.
--
2.20.1