Patch "NFS: revalidate "." etc correctly on "open"." has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

NFS: revalidate "." etc correctly on "open".

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
nfs-revalidate-.-etc-correctly-on-open.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: NeilBrown <[email protected]>
Date: Fri, 25 Aug 2017 17:34:41 +1000
Subject: NFS: revalidate "." etc correctly on "open".

From: NeilBrown <[email protected]>

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.

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

@@ -1266,7 +1266,7 @@ 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;

@@ -1426,6 +1426,7 @@ 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,

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/nfs-revalidate-.-etc-correctly-on-open.patch