Re: [PATCH] nfsd: revoking of suid/sgid bits after chown() in a consistent way

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Dec 11, 2013 at 03:00:22PM +0400, Stanislav Kholmanskikh wrote:
> 
> 
> On 12/11/2013 02:16 PM, Stanislav Kholmanskikh wrote:
> [cut off]
> >
> >This patch makes NFS to behave like local file systems.
> >
> [cut off]
> 
> This patch allows to run generic/193 without any issues with NFSv3.
> 
> With NFSv4 generic/193 fails (but with the other issues, which
> existed even before the patch).
> 
> generic/193 expects that suid/sgid bits are cleared after the file
> truncation:
> 
> touch file
> chown fsgqa:fsgqa file
> chmod u+s file
> echo 'xyz' > file
> ls -l file
> su fsgqa -c 'echo > file'
> ls -l file
> 
> With ext4 (for example), we have expectable results:
> -rwSr--r-- 1 fsgqa fsgqa 4 Dec 11 05:21 file
> -rw-r--r-- 1 fsgqa fsgqa 1 Dec 11 05:22 file
> 
> With NFSv3 as well:
> -rwSr--r-- 1 fsgqa fsgqa 4 Dec 11 05:24 file
> -rw-r--r-- 1 fsgqa fsgqa 1 Dec 11 05:25 file
> 
> But with NFSv4 the bits are not cleared:
> -rwSr--r-- 1 fsgqa fsgqa 1 Dec 11 05:19 file
> -rwSr--r-- 1 fsgqa fsgqa 1 Dec 11 05:21 file
> 
> 'echo > file' issues:
> 
> open("file", O_WRONLY|O_CREAT|O_TRUNC, 0666)
> 
> Can it be because of design differences between NFSv3 and NFSv4?

In the v3 case I'd expect the open O_TRUNC to result in a SETATTR rpc,
in the v4 case an OPEN rpc.  Both result in a call to nfsd_setattr,
though I only see nfsd_setattr turning off the SUID/SGID bits in the
chown case.  Are you sure it isn't the subsequent write that clears
those bits?

But looks to me like nfsd_vfs_write (used in both v3 & v4 cases) clears
suid & guid, so I still don't see it.

--b.