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From:   Wolfgang Walter <linux@stwm.de>
To:     stable@vger.kernel.org
Cc:     gregkh@linuxfoundation.org,
        Ben Hutchings <ben.hutchings@codethink.co.uk>,
        linux-kernel@vger.kernel.org
Subject: Re: NFS: regression in stable kernel 4.9.78 from 4.9.75
Date:   Mon, 29 Jan 2018 14:42:49 +0100
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Hello!

Am Montag, 29. Januar 2018, 13:22:49 schrieb Wolfgang Walter:
> Hello,
> 
> after upgrading our nfs-server from  4.9.75 to 4.9.78 group permissions stop
> working (for clients). If you need group permissions to access a file or
> directory, sometimes access is granted, but rather often denied. Often
> access to the same object is denied within seconds after access was granted
> in an earlier access. user permissions work fine.
> 
> Downgrading to 4.9.75 fixes the issue.
> 
> We use kerberos.
> 
> Regards,

This seems to be fixed in 4.15 with commit 
1995266727fa8143897e89b55f5d3c79aa828420:


commit 1995266727fa8143897e89b55f5d3c79aa828420
Author: Ben Hutchings <ben.hutchings@codethink.co.uk>
Date:   Mon Jan 22 20:11:06 2018 +0000

    nfsd: auth: Fix gid sorting when rootsquash enabled
    
    Commit bdcf0a423ea1 ("kernel: make groups_sort calling a responsibility
    group_info allocators") appears to break nfsd rootsquash in a pretty
    major way.
    
    It adds a call to groups_sort() inside the loop that copies/squashes
    gids, which means the valid gids are sorted along with the following
    garbage.  The net result is that the highest numbered valid gids are
    replaced with any lower-valued garbage gids, possibly including 0.
    
    We should sort only once, after filling in all the gids.
    
    Fixes: bdcf0a423ea1 ("kernel: make groups_sort calling a responsibility 
...")
    Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
    Acked-by: J. Bruce Fields <bfields@redhat.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>


So this should be applied to stables 4.4, 4.9 and 4.14 (and others where 
bdcf0a423ea1 has been backported to).

Regards,
-- 
Wolfgang Walter
Studentenwerk M?nchen
Anstalt des ?ffentlichen Rechts