Re: linux-3.14 nfsd regression

J. Bruce Fields
2014-04-04T13:58:49Z

On Thu, Apr 03, 2014 at 07:21:46PM -0400, Jeff Layton wrote:
> So according to the RFC you have to encode both the mode bits and the
> ftype for v2. The type bits seem to be removed from the mode in NFSv3
> though, so perhaps we should only be doing that masking in versions
> above v2?

Right, the problematic patch applied the same mask in both v2 and v3
cases, so I'm reverting just the v2 part (see below).

> With a quick check, it looks like the v3 code doesn't rely on those bits
> and I imagine v4 doesn't either.
>
> It might also be nice to have the client v2 decode_fattr function to
> throw a warning if the server sends us mismatched type bits and ftype
> values. That would have helped us catch this sooner...

Yes, that might be a reasonable thing to do, though I don't know if it's
worth it.

--b.

commit 35a8dff14e76c00e5b52140290cfb498dc2454a0
Author: J. Bruce Fields <bfields@redhat.com>
Date: Thu Apr 3 15:10:35 2014 -0400

nfsd: revert v2 half of "nfsd: don't return high mode bits"

This reverts the part of commit 6e14b46b91fee8a049b0940333ce13a820beaaa5
that changes NFSv2 behavior.

Mark Lord found that it broke nfs-root for Linux clients, because it
broke NFSv2.

In fact, from RFC 1094:

"Notice that the file type is specified both in the mode bits
and in the file type. This is really a bug in the protocol and
will be fixed in future versions."

So NFSv2 clients really are expected to depend on the high bits of the
mode.

Cc: stable@kernel.org
Reported-by: Mark Lord <mlord@pobox.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
index b17d932..9c769a4 100644
--- a/fs/nfsd/nfsxdr.c
+++ b/fs/nfsd/nfsxdr.c
@@ -152,7 +152,7 @@ encode_fattr(struct svc_rqst *rqstp, __be32 *p, struct svc_fh *fhp,
type = (stat->mode & S_IFMT);

*p++ = htonl(nfs_ftypes[type >> 12]);
- *p++ = htonl((u32) (stat->mode & S_IALLUGO));
+ *p++ = htonl((u32) stat->mode);
*p++ = htonl((u32) stat->nlink);
*p++ = htonl((u32) from_kuid(&init_user_ns, stat->uid));
*p++ = htonl((u32) from_kgid(&init_user_ns, stat->gid));