linux-kernel - Re: linux-3.14 nfsd regression

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Date:	Fri, 4 Apr 2014 09:58:43 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	Mark Lord <mlord@...ox.com>,
	"J. Bruce Fields" <bfields@...hat.com>, Albert Fluegel <af@....de>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: linux-3.14 nfsd regression

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@...hat.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@...nel.org
    Reported-by: Mark Lord <mlord@...ox.com>
    Signed-off-by: J. Bruce Fields <bfields@...hat.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));
--
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