From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45726C282C8 for ; Mon, 28 Jan 2019 20:23:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 171CB21783 for ; Mon, 28 Jan 2019 20:23:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727250AbfA1UXm (ORCPT ); Mon, 28 Jan 2019 15:23:42 -0500 Received: from www62.your-server.de ([213.133.104.62]:44724 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726993AbfA1UXl (ORCPT ); Mon, 28 Jan 2019 15:23:41 -0500 Received: from [178.197.249.35] (helo=localhost) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1goDRU-0003ZW-4J; Mon, 28 Jan 2019 21:23:40 +0100 From: Daniel Borkmann To: gregkh@linuxfoundation.org Cc: ast@kernel.org, stable@vger.kernel.org, Daniel Borkmann Subject: [PATCH stable 4.20 07/10] bpf: fix check_map_access smin_value test when pointer contains offset Date: Mon, 28 Jan 2019 21:23:27 +0100 Message-Id: <20190128202330.32664-8-daniel@iogearbox.net> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20190128202330.32664-1-daniel@iogearbox.net> References: <20190128202330.32664-1-daniel@iogearbox.net> X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.100.2/25339/Mon Jan 28 19:32:47 2019) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org [ commit b7137c4eab85c1cf3d46acdde90ce1163b28c873 upstream ] In check_map_access() we probe actual bounds through __check_map_access() with offset of reg->smin_value + off for lower bound and offset of reg->umax_value + off for the upper bound. However, even though the reg->smin_value could have a negative value, the final result of the sum with off could be positive when pointer arithmetic with known and unknown scalars is combined. In this case we reject the program with an error such as "R min value is negative, either use unsigned index or do a if (index >=0) check." even though the access itself would be fine. Therefore extend the check to probe whether the actual resulting reg->smin_value + off is less than zero. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 072e0416ac56..2018c190bd36 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1370,13 +1370,17 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno, */ if (env->log.level) print_verifier_state(env, state); + /* The minimum value is only important with signed * comparisons where we can't assume the floor of a * value is 0. If we are using signed variables for our * index'es we need to make sure that whatever we use * will have a set floor within our range. */ - if (reg->smin_value < 0) { + if (reg->smin_value < 0 && + (reg->smin_value == S64_MIN || + (off + reg->smin_value != (s64)(s32)(off + reg->smin_value)) || + reg->smin_value + off < 0)) { verbose(env, "R%d min value is negative, either use unsigned index or do a if (index >=0) check.\n", regno); return -EACCES; -- 2.17.1