From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:48252 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727510AbeJIB74 (ORCPT ); Mon, 8 Oct 2018 21:59:56 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Borkmann , John Fastabend , Alexei Starovoitov , Sasha Levin Subject: [PATCH 4.18 029/168] bpf: fix shift upon scatterlist ring wrap-around in bpf_msg_pull_data Date: Mon, 8 Oct 2018 20:30:09 +0200 Message-Id: <20181008175621.153149806@linuxfoundation.org> In-Reply-To: <20181008175620.043587728@linuxfoundation.org> References: <20181008175620.043587728@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann [ Upstream commit 2e43f95dd8ee62bc8bf57f2afac37fbd70c8d565 ] If first_sg and last_sg wraps around in the scatterlist ring, then we need to account for that in the shift as well. E.g. crafting such msgs where this is the case leads to a hang as shift becomes negative. E.g. consider the following scenario: first_sg := 14 |=> shift := -12 msg->sg_start := 10 last_sg := 3 | msg->sg_end := 5 round 1: i := 15, move_from := 3, sg[15] := sg[ 3] round 2: i := 0, move_from := -12, sg[ 0] := sg[-12] round 3: i := 1, move_from := -11, sg[ 1] := sg[-11] round 4: i := 2, move_from := -10, sg[ 2] := sg[-10] [...] round 13: i := 11, move_from := -1, sg[ 2] := sg[ -1] round 14: i := 12, move_from := 0, sg[ 2] := sg[ 0] round 15: i := 13, move_from := 1, sg[ 2] := sg[ 1] round 16: i := 14, move_from := 2, sg[ 2] := sg[ 2] round 17: i := 15, move_from := 3, sg[ 2] := sg[ 3] [...] This means we will loop forever and never hit the msg->sg_end condition to break out of the loop. When we see that the ring wraps around, then the shift should be MAX_SKB_FRAGS - first_sg + last_sg - 1. Meaning, the remainder slots from the tail of the ring and the head until last_sg combined. Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data") Signed-off-by: Daniel Borkmann Acked-by: John Fastabend Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/core/filter.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2360,7 +2360,10 @@ BPF_CALL_4(bpf_msg_pull_data, * had a single entry though we can just replace it and * be done. Otherwise walk the ring and shift the entries. */ - shift = last_sg - first_sg - 1; + WARN_ON_ONCE(last_sg == first_sg); + shift = last_sg > first_sg ? + last_sg - first_sg - 1 : + MAX_SKB_FRAGS - first_sg + last_sg - 1; if (!shift) goto out;