Patch "NFS: only invalidate dentrys that are clearly invalid." has been added to the 4.12-stable tree

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

NFS: only invalidate dentrys that are clearly invalid.

to the 4.12-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-only-invalidate-dentrys-that-are-clearly-invalid.patch
and it can be found in the queue-4.12 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: Wed, 5 Jul 2017 12:22:20 +1000
Subject: NFS: only invalidate dentrys that are clearly invalid.

From: NeilBrown <[email protected]>

commit cc89684c9a265828ce061037f1f79f4a68ccd3f7 upstream.

Since commit bafc9b754f75 ("vfs: More precise tests in d_invalidate") in v3.18, a return of '0' from ->d_revalidate() will cause the dentry to be invalidated even if it has filesystems mounted on or it or on a descendant. The mounted filesystem is unmounted.

This means we need to be careful not to return 0 unless the directory referred to truly is invalid. So -ESTALE or -ENOENT should invalidate the directory. Other errors such a -EPERM or -ERESTARTSYS should be returned from ->d_revalidate() so they are propagated to the caller.

A particular problem can be demonstrated by:

1/ mount an NFS filesystem using NFSv3 on /mnt
2/ mount any other filesystem on /mnt/foo
3/ ls /mnt/foo
4/ turn off network, or otherwise make the server unable to respond 5/ ls /mnt/foo &
6/ cat /proc/$!/stack # note that nfs_lookup_revalidate is in the call stack 7/ kill -9 $! # this results in -ERESTARTSYS being returned
8/ observe that /mnt/foo has been unmounted.

This patch changes nfs_lookup_revalidate() to only treat
-ESTALE from nfs_lookup_verify_inode() and -ESTALE or -ENOENT from ->lookup()
as indicating an invalid inode. Other errors are returned.

Also nfs_check_inode_attributes() is changed to return -ESTALE rather than -EIO. This is consistent with the error returned in similar circumstances from nfs_update_inode().

As this bug allows any user to unmount a filesystem mounted on an NFS filesystem, this fix is suitable for stable kernels.

---
 fs/nfs/dir.c   |   12 ++++++++----
 fs/nfs/inode.c |    4 ++--
 2 files changed, 10 insertions(+), 6 deletions(-)

@@ -1115,11 +1115,13 @@ static int nfs_lookup_revalidate(struct
 	/* Force a full look up iff the parent directory has changed */
 	if (!nfs_is_exclusive_create(dir, flags) &&
 	    nfs_check_verifier(dir, dentry, flags & LOOKUP_RCU)) {
-
-		if (nfs_lookup_verify_inode(inode, flags)) {
+		error = nfs_lookup_verify_inode(inode, flags);
+		if (error) {
 			if (flags & LOOKUP_RCU)
 				return -ECHILD;
-			goto out_zap_parent;
+			if (error == -ESTALE)
+				goto out_zap_parent;
+			goto out_error;
 		}
 		nfs_advise_use_readdirplus(dir);
 		goto out_valid;

@@ -1144,8 +1146,10 @@ static int nfs_lookup_revalidate(struct
 	trace_nfs_lookup_revalidate_enter(dir, dentry, flags);
 	error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, fhandle, fattr, label);
 	trace_nfs_lookup_revalidate_exit(dir, dentry, flags, error);
-	if (error)
+	if (error == -ESTALE || error == -ENOENT)
 		goto out_bad;
+	if (error)
+		goto out_error;
 	if (nfs_compare_fh(NFS_FH(inode), fhandle))
 		goto out_bad;
 	if ((error = nfs_refresh_inode(inode, fattr)) != 0)

@@ -1315,9 +1315,9 @@ static int nfs_check_inode_attributes(st
 		return 0;
 	/* Has the inode gone and changed behind our back? */
 	if ((fattr->valid & NFS_ATTR_FATTR_FILEID) && nfsi->fileid != fattr->fileid)
-		return -EIO;
+		return -ESTALE;
 	if ((fattr->valid & NFS_ATTR_FATTR_TYPE) && (inode->i_mode & S_IFMT) != (fattr->mode & S_IFMT))
-		return -EIO;
+		return -ESTALE;
 
 	if (!nfs_file_has_buffered_writers(nfsi)) {
 		/* Verify a few of the more important attributes */

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

queue-4.12/nfs-only-invalidate-dentrys-that-are-clearly-invalid.patch queue-4.12/md-don-t-use-flush_signals-in-userspace-processes.patch queue-4.12/md-fix-deadlock-between-mddev_suspend-and-md_write_start.patch queue-4.12/net-sunrpc-xprt_sock-fix-regression-in-connection-error-reporting.patch