From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754561AbbHBANG (ORCPT ); Sat, 1 Aug 2015 20:13:06 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35940 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751716AbbHBAJr (ORCPT ); Sat, 1 Aug 2015 20:09:47 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "Willem de Bruijn" , "David S. Miller" Date: Sun, 02 Aug 2015 01:02:38 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 138/164] packet: avoid out of bounds read in round robin fanout In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.70-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Willem de Bruijn [ Upstream commit 468479e6043c84f5a65299cc07cb08a22a28c2b1 ] PACKET_FANOUT_LB computes f->rr_cur such that it is modulo f->num_members. It returns the old value unconditionally, but f->num_members may have changed since the last store. Ensure that the return value is always < num. When modifying the logic, simplify it further by replacing the loop with an unconditional atomic increment. Fixes: dc99f600698d ("packet: Add fanout support.") Suggested-by: Eric Dumazet Signed-off-by: Willem de Bruijn Acked-by: Eric Dumazet Signed-off-by: David S. Miller [bwh: Backported to 3.2: - Adjust context - Demux functions return a sock pointer, not an index] Signed-off-by: Ben Hutchings --- net/packet/af_packet.c | 18 ++---------------- 1 file changed, 2 insertions(+), 16 deletions(-) --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1170,16 +1170,6 @@ static void packet_sock_destruct(struct sk_refcnt_debug_dec(sk); } -static int fanout_rr_next(struct packet_fanout *f, unsigned int num) -{ - int x = atomic_read(&f->rr_cur) + 1; - - if (x >= num) - x = 0; - - return x; -} - static struct sock *fanout_demux_hash(struct packet_fanout *f, struct sk_buff *skb, unsigned int num) { u32 idx, hash = skb->rxhash; @@ -1191,13 +1181,9 @@ static struct sock *fanout_demux_hash(st static struct sock *fanout_demux_lb(struct packet_fanout *f, struct sk_buff *skb, unsigned int num) { - int cur, old; + unsigned int val = atomic_inc_return(&f->rr_cur); - cur = atomic_read(&f->rr_cur); - while ((old = atomic_cmpxchg(&f->rr_cur, cur, - fanout_rr_next(f, num))) != cur) - cur = old; - return f->arr[cur]; + return f->arr[val % num]; } static struct sock *fanout_demux_cpu(struct packet_fanout *f, struct sk_buff *skb, unsigned int num)