linux-kernel - Re: [NFS] NFSv2/3 broken exporting/mounting (permission denied) in 2.6.24-rc4

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Message-ID: <20071207200655.GD2204@fieldses.org>
Date:	Fri, 7 Dec 2007 15:06:55 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Erez Zadok <ezk@...sunysb.edu>
Cc:	linux-kernel@...r.kernel.org, nfs@...ts.sourceforge.net,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [NFS] NFSv2/3 broken exporting/mounting (permission denied) in
	2.6.24-rc4

On Fri, Dec 07, 2007 at 03:00:13PM -0500, Erez Zadok wrote:
> In message <20071207025504.GA3070@...ldses.org>, "J. Bruce Fields" writes:
> > On Thu, Dec 06, 2007 at 09:20:41PM -0500, Erez Zadok wrote:
> > > I get a "permission denied" when trying to mount a localhost nfsv2/3
> > > exported volume, on v2.6.24-rc4-124-gf194d13.  It works w/ nfsv4 mounting.
> > > It worked fine in 2.6.24-rc3.  Here's a sequence of ops I tried:
> > > 
> > > # mount -t ext2 /dev/hdb1 /n/lower/b0
> > > # exportfs -o no_root_squash,rw localhost:/n/lower/b0
> > > # mount -t nfs -o nfsvers=3 localhost:/n/lower/b0 /mnt
> > 
> > What do you see if you watch the network traffic in ethereal?
> > 
> > --b.
> 
> Bruce, I'm using nfs-utils-1.0.10-14.fc6 on an FC6 system with all latest
> FC6 patches.  Using git-bisect I was able to find the patch which broke it:

Wow, thanks for your work finding that.

> 
> commit 2b1e300a9dfc3196ccddf6f1d74b91b7af55e416
> Author: Eric W. Biederman <ebiederm@...ssion.com>
> Date:   Sun Dec 2 00:33:17 2007 +1100
> 
>     [NETNS]: Fix /proc/net breakage
>     
>     Well I clearly goofed when I added the initial network namespace support
>     for /proc/net.  Currently things work but there are odd details visible to
>     user space, even when we have a single network namespace.
>     
>     Since we do not cache proc_dir_entry dentries at the moment we can just
>     modify ->lookup to return a different directory inode depending on the
>     network namespace of the process looking at /proc/net, replacing the
>     current technique of using a magic and fragile follow_link method.
>     
>     To accomplish that this patch:
>     - introduces a shadow_proc method to allow different dentries to
>       be returned from proc_lookup.
>     - Removes the old /proc/net follow_link magic
>     - Fixes a weakness in our not caching of proc generic dentries.
>     
>     As shadow_proc uses a task struct to decided which dentry to return we can
>     go back later and fix the proc generic caching without modifying any code
>     that uses the shadow_proc method.
>     
>     Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
>     Cc: "Rafael J. Wysocki" <rjw@...k.pl>
>     Cc: Pavel Machek <pavel@....cz>
>     Cc: Pavel Emelyanov <xemul@...nvz.org>
>     Cc: "David S. Miller" <davem@...emloft.net>
>     Cc: Ingo Molnar <mingo@...e.hu>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>     Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
> 
> With the above patch, rpc.mountd is unable to open /proc/fs/nfsd/filehandle.
> Strace shows:
> 
> open("/proc/fs/nfsd/filehandle", O_RDWR|O_LARGEFILE) = -1 ENOENT (No such file or directory)
> 
> Without the above patch, /proc/fs/nfsd is populated with a number of files,
> including "filehandle".

Those files are actually in a separate filesystem (of type "nfsd") which
is supposed to be mounted on /proc/fs/nfsd/.   So that mount must have
failed in the bad case?  It's not immediately obvious to me what this
patch has to do with that.  Hm.

--b.
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