Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

[Matthias Andree]

(Please consider removing FreeBSD-stable from the recipient list when
replying.)

Summary:

The Linux 2.2.18 NFS v3 server returns bogus and as per RFC-1813 invalid
NFS3ERR_ROFS to ACCESS procedure calls when exporting a file system
read-only, when it should instead return "OK" along with the actual
permissions the client has, ANDed with the permissions the client
queried. 

The bug is visible on FreeBSD 4.2-STABLE client which cannot ls The
mounted file system (NFS v2 is fine since it does not have ACCESS).
There is no related log entry in the 2.2.19pre7 change log.  I did not
check Linux 2.4.0, 2.4.0-acX or 2.4.1-preX either.

On Tue, 23 Jan 2001, Guy Harris wrote:

> Yes - for one thing, that means that if some client decides, while it's
> asking whether the server whether it can write to a file, to check also
> whether it can read from the file, it can get back an answer to both of
> those questions, even if the file is on a read-only file system.

Yup. Looks like a Linux kernel bug, so I'm cc'ing Alan Cox as kernel
release maintainer as well as linux-kernel to make this a known issue.

I got libpcap 0.6.1 and ethereal 0.8.15 and that's what I found:

FreeBSD 4.2-STABLE sends three NFSPROC3_ACCESS requests, with 0x3f
argument (meaning READ|LOOKUP|MODIFY|EXTEND|DELETE|EXECUTE), and to
each, Linux 2.2.18 sends NFS3ERR_ROFS back, obj_attributes contains the
stat data. ERR_ROFS is invalid here and makes indeed no sense, proper
behaviour would be NFS3_OK with just READ|LOOKUP|EXECUTE set, since the
server can actually access or stat the exported FS. Please correct me if
I'm mistaking what RFC 1813 demands.

client: $ mount server:/space /mnt
        $ ls /mnt
        ls: mnt: Read-only file system
        (FreeBSD 4.2-STABLE)

server: $ ls -ld /space/
        drwxrwxrwt  23 root     root          706 Jan  2 11:53 /space/
        $ grep /space /etc/exports
        /space 192.168.0.0/255.255.255.0(ro)
        (Linux 2.2.18, nfs-utils 0.2.1)

-- 
Matthias Andree
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Re: [NFS] Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

[Neil Brown]

On Wednesday January 24, matthias.andree@stud.uni-dortmund.de wrote:
> (Please consider removing FreeBSD-stable from the recipient list when
> replying.)
freebsd-stable removed!  reiserfs gone. Who goes next:-? Alan?
> 
> Summary:
> 
> The Linux 2.2.18 NFS v3 server returns bogus and as per RFC-1813 invalid
> NFS3ERR_ROFS to ACCESS procedure calls when exporting a file system
> read-only, when it should instead return "OK" along with the actual
> permissions the client has, ANDed with the permissions the client
> queried. 
> 
> The bug is visible on FreeBSD 4.2-STABLE client which cannot ls The
> mounted file system (NFS v2 is fine since it does not have ACCESS).
> There is no related log entry in the 2.2.19pre7 change log.  I did not
> check Linux 2.4.0, 2.4.0-acX or 2.4.1-preX either.

To summarise the summary of the summary:
I stuffed up when I tried to interpret the error, but after much
sensible correction, here is a patch.  Please try it, and suggest any
other errs that should be tested for (or maybe we should invert the
sense of the test, and test for error codes that ACCESS is allowed to
return.
2.4.0 seems to get it right.

NeilBrown

--- ./fs/nfsd/vfs.c	2001/01/10 05:03:28	1.11
+++ ./fs/nfsd/vfs.c	2001/01/24 06:02:01
@@ -448,7 +448,9 @@
 			error = nfsd_permission(export, dentry, (map->how | NO_OWNER_OVERRIDE));
 			if (error == 0)
 				result |= map->access;
-			else if ((error == nfserr_perm) || (error == nfserr_acces)) {
+			else if ((error == nfserr_perm) ||
+				 (error == nfserr_acces) ||
+				 (error == nfserr_rofs)) {
 				/*
 				 *  This access type is denyed; but the 
 				 *  access query itself succeeds.

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Re: [NFS] Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

[Matthias Andree]

On Wed, 24 Jan 2001, Neil Brown wrote:

> freebsd-stable removed!  reiserfs gone. Who goes next:-? Alan?

The bugs, I hope.

> I stuffed up when I tried to interpret the error, but after much
> sensible correction, here is a patch.  Please try it, and suggest any
> other errs that should be tested for (or maybe we should invert the
> sense of the test, and test for error codes that ACCESS is allowed to
> return.

This looks better and it makes FreeBSD able to ls the directory, and on
touch /mnt/try, I get EROFS on the client, so this is okay; however, the
access reply does not include EXECUTE permissions which I find strange,
since the client lists this:

drwxrwxrwt  23 root  wheel  706 Jan  2 11:53 /mnt

Evidently, the directory has execution permissions for everyone.

-- 
Matthias Andree
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Re: [NFS] Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

[Matthias Andree]

On Wed, 24 Jan 2001, Matthias Andree wrote:

> This looks better and it makes FreeBSD able to ls the directory, and on
> touch /mnt/try, I get EROFS on the client, so this is okay; however, the
> access reply does not include EXECUTE permissions which I find strange,
> since the client lists this:
> 

My fault. NFSv3 has a different permission partitioning than local file
systems have, I did not see that. So Linux does the right
thing for ACCESS with Neil's patch. Neil, could you submit that patch to
Alan or bless it for inclusion into 2.2.19(pre)? The FreeBSD people
could then sleep well again. :-)
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Re: [NFS] Linux 2.2.18 nfs v3 server bug (was: Incompatible: FreeBSD 4.2 client, Linux 2.2.18 nfsv3 server, read-only export)

[Neil Brown]

On Thursday January 25, matthias.andree@stud.uni-dortmund.de wrote:
> On Wed, 24 Jan 2001, Matthias Andree wrote:
> 
> > This looks better and it makes FreeBSD able to ls the directory, and on
> > touch /mnt/try, I get EROFS on the client, so this is okay; however, the
> > access reply does not include EXECUTE permissions which I find strange,
> > since the client lists this:
> > 
> 
> My fault. NFSv3 has a different permission partitioning than local file
> systems have, I did not see that. So Linux does the right
> thing for ACCESS with Neil's patch. Neil, could you submit that patch to
> Alan or bless it for inclusion into 2.2.19(pre)? The FreeBSD people
> could then sleep well again. :-)

I have sent bunch of patches to Alan some weeks ago, but no 2.2.19pre
release has appeared since.  When the 2.2.19pre series gets going
again, I will certainly sent this patch, and a few others that I have
collected.

NeilBrown
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