[PATCH 4.9 36/38] NFS: revalidate "." etc correctly on "open".

Greg Kroah-Hartman
2017-12-04T16:30:00Z

From: NeilBrown <neilb@suse.com>

commit b688741cb06695312f18b730653d6611e1bad28d upstream.

For correct close-to-open semantics, NFS must validate
the change attribute of a directory (or file) on open.

Since commit ecf3d1f1aa74 ("vfs: kill FS_REVAL_DOT by adding a
d_weak_revalidate dentry op"), open() of "." or a path ending ".." is
not revalidated reliably (except when that direct is a mount point).

Prior to that commit, "." was revalidated using nfs_lookup_revalidate()
which checks the LOOKUP_OPEN flag and forces revalidation if the flag is
set.
Since that commit, nfs_weak_revalidate() is used for NFSv3 (which
ignores the flags) and nothing is used for NFSv4.

This is fixed by using nfs_lookup_verify_inode() in
nfs_weak_revalidate(). This does the revalidation exactly when needed.
Also, add a definition of .d_weak_revalidate for NFSv4.

The incorrect behavior is easily demonstrated by running "echo *" in
some non-mountpoint NFS directory while watching network traffic.
Without this patch, "echo *" sometimes doesn't produce any traffic.
With the patch it always does.

Fixes: ecf3d1f1aa74 ("vfs: kill FS_REVAL_DOT by adding a d_weak_revalidate dentry op")
cc: stable@vger.kernel.org (3.9+)
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/nfs/dir.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1292,7 +1292,7 @@ static int nfs_weak_revalidate(struct de
return 0;
}

- error = nfs_revalidate_inode(NFS_SERVER(inode), inode);
+ error = nfs_lookup_verify_inode(inode, flags);
dfprintk(LOOKUPCACHE, "NFS: %s: inode %lu is %s\n",
__func__, inode->i_ino, error ? "invalid" : "valid");
return !error;
@@ -1443,6 +1443,7 @@ static int nfs4_lookup_revalidate(struct

const struct dentry_operations nfs4_dentry_operations = {
.d_revalidate = nfs4_lookup_revalidate,
+ .d_weak_revalidate = nfs_weak_revalidate,
.d_delete = nfs_dentry_delete,
.d_iput = nfs_dentry_iput,
.d_automount = nfs_d_automount,