linux-kernel - [PATCH 3.16 114/305] sunrpc: fix stripping of padded MIC tokens

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Message-ID: <lsq.1471110171.676127860@decadent.org.uk>
Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Tomáš Trnka" <ttrnka@...l.muni.cz>,
	"J. Bruce Fields" <bfields@...hat.com>,
	"Jeff Layton" <jlayton@...chiereds.net>
Subject: [PATCH 3.16 114/305] sunrpc: fix stripping of padded MIC tokens

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Tomáš Trnka <ttrnka@...l.muni.cz>

commit c0cb8bf3a8e4bd82e640862cdd8891400405cb89 upstream.

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").

Fixes: 4c190e2f913f "unrpc: trim off trailing checksum..."
Signed-off-by: Tomáš Trnka <ttrnka@...l.muni.cz>
Acked-by: Jeff Layton <jlayton@...chiereds.net>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/sunrpc/auth_gss/svcauth_gss.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -855,8 +855,8 @@ unwrap_integ_data(struct svc_rqst *rqstp
 		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);