Re: [PATCH] sunrpc: fix stripping of padded MIC tokens

[bfields@fieldses.org (J. Bruce Fields)]

On Fri, May 20, 2016 at 11:31:13AM -0400, Jeff Layton wrote:
> On Fri, 2016-05-20 at 16:41 +0200, Tomáš Trnka wrote:
> > The length of the GSS MIC token need not be a multiple of four bytes.
> > It is then padded by XDR to a multiple of 4 B, but unwrap_integ_data()
> > would previously only trim mic.len + 4 B. The remaining up to three
> > bytes would then trigger a check in nfs4svc_decode_compoundargs(),
> > leading to a "garbage args" error and mount failure:
> > 
> > nfs4svc_decode_compoundargs: compound not properly padded!
> > nfsd: failed to decode arguments!
> > 
> > This would prevent older clients using the pre-RFC 4121 MIC format
> > (37-byte MIC including a 9-byte OID) from mounting exports from v3.9+
> > servers using krb5i.
> > 
> > The trimming was introduced by commit 4c190e2f913f ("sunrpc: trim off
> > trailing checksum before returning decrypted or integrity authenticated
> > buffer").
> > 
> > Signed-off-by: Tomáš Trnka <ttrnka@mail.muni.cz>
> > ---
> >  net/sunrpc/auth_gss/svcauth_gss.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/sunrpc/auth_gss/svcauth_gss.c 
> > b/net/sunrpc/auth_gss/svcauth_gss.c
> > index 1095be9..4605dc7 100644
> > --- a/net/sunrpc/auth_gss/svcauth_gss.c
> > +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> > @@ -857,8 +857,8 @@ unwrap_integ_data(struct svc_rqst *rqstp, struct xdr_buf 
> > *buf, u32 seq, struct g
> >  		goto out;
> >  	if (svc_getnl(&buf->head[0]) != seq)
> >  		goto out;
> > -	/* trim off the mic at the end before returning */
> > -	xdr_buf_trim(buf, mic.len + 4);
> > +	/* trim off the mic and padding at the end before returning */
> > +	xdr_buf_trim(buf, round_up_to_quad(mic.len) + 4);
> >  	stat = 0;
> >  out:
> >  	kfree(mic.data);
> 
> Looks reasonable:
> 
> Acked-by: Jeff Layton <jlayton@poochiereds.net>

Thanks!  Applying for 4.6 and stable.

--b.