Re: [PATCH] sunrpc: sort groups on unix_gid_parse

[Thiago Rafael Becker <thiago.becker@gmail.com>]

On Mon, 27 Nov 2017, J. Bruce Fields wrote:

> Thanks for the patch:
>
> On Mon, Nov 27, 2017 at 05:25:08PM -0200, Thiago Rafael Becker wrote:
>> In cases were mountd is managing the group membership for nfsd,
>> if a user has several groups, multiple nfsd threads may call
>> sort_groups for the same freshly created unix_gid_cache entry
>> simultaneously, causing entries to be overwritten and the cache
>> entry to get corrupted.
>
> The groups_sort call is in set_groups, called from
> fs/nfsd/auth.c:nfsd_setuser():
>
> 	set_groups(new, gi);
>
> where "gi" is usually (in the absence of id squashing) a pointer to
> rqstp->rq_cred.cr_group_info, which can be in use by other threads.
>
> To me it's pretty unintuitive that set_groups() would modify the group
> info passed in the second argument.  While we're here, I wonder if we
> should make that the caller's responsibility?  There are basically only
> three callers outside this one.
>
> But I'm OK with this patch.  I probably need an OK from a vfs person to
> take it through the nfsd tree?
>
> --b.

I tend to agree. I have an updated version of the patches that I'll be 
sending to a broader audience to see if they have any inputs.