From patchwork Thu Apr 4 06:22:41 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrey Ignatov X-Patchwork-Id: 1076856 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=fb.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=fb.com header.i=@fb.com header.b="Mvfy37tA"; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 44ZXvK1YkKz9sRW for ; Thu, 4 Apr 2019 17:23:25 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726942AbfDDGXW (ORCPT ); Thu, 4 Apr 2019 02:23:22 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:47306 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726886AbfDDGXV (ORCPT ); Thu, 4 Apr 2019 02:23:21 -0400 Received: from pps.filterd (m0044012.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x346FlLx005875 for ; Wed, 3 Apr 2019 23:23:20 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=fLYcvqDDfRxBmDq7oBbGRebVZnSSoGyk9Zd20bGNmpc=; b=Mvfy37tAPTAQDeRD+wZxrpyKM83kjsryLTnWH4HFa1RCzDQ8edYYiX2pdz/5yKEPhT6J tgiFCW4Csa9rfO7s+cv3zEtnmB99WV8wOlMmxtVwMd7QZn41QVIFVsy1ZqJII5d17Xlu S8spwCcOxMwDbTJingpud78xxvkb+Owi/3c= Received: from mail.thefacebook.com ([199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 2rn548985k-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT) for ; Wed, 03 Apr 2019 23:23:20 -0700 Received: from mx-out.facebook.com (2620:10d:c081:10::13) by mail.thefacebook.com (2620:10d:c081:35::129) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA) id 15.1.1713.5; Wed, 3 Apr 2019 23:23:18 -0700 Received: by dev082.prn2.facebook.com (Postfix, from userid 572249) id D963E3702EB4; Wed, 3 Apr 2019 23:23:17 -0700 (PDT) Smtp-Origin-Hostprefix: dev From: Andrey Ignatov Smtp-Origin-Hostname: dev082.prn2.facebook.com To: CC: Andrey Ignatov , , , Smtp-Origin-Cluster: prn2c23 Subject: [PATCH v3 bpf-next 5/7] bpf: Sanity check max value for var_off stack access Date: Wed, 3 Apr 2019 23:22:41 -0700 Message-ID: <08f3da8fb4b08e5ee6d12985ccbef8a7702a000f.1554358433.git.rdna@fb.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: References: X-FB-Internal: Safe MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-04-04_03:, , signatures=0 X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org As discussed in [1] max value of variable offset has to be checked for overflow on stack access otherwise verifier would accept code like this: 0: (b7) r2 = 6 1: (b7) r3 = 28 2: (7a) *(u64 *)(r10 -16) = 0 3: (7a) *(u64 *)(r10 -8) = 0 4: (79) r4 = *(u64 *)(r1 +168) 5: (c5) if r4 s< 0x0 goto pc+4 R1=ctx(id=0,off=0,imm=0) R2=inv6 R3=inv28 R4=inv(id=0,umax_value=9223372036854775807,var_off=(0x0; 0x7fffffffffffffff)) R10=fp0,call_-1 fp-8=mmmmmmmm fp-16=mmmmmmmm 6: (17) r4 -= 16 7: (0f) r4 += r10 8: (b7) r5 = 8 9: (85) call bpf_getsockopt#57 10: (b7) r0 = 0 11: (95) exit , where R4 obviosly has unbounded max value. Fix it by checking that reg->smax_value is inside (-BPF_MAX_VAR_OFF; BPF_MAX_VAR_OFF) range. reg->smax_value is used instead of reg->umax_value because stack pointers are calculated using negative offset from fp. This is opposite to e.g. map access where offset must be non-negative and where umax_value is used. Also dedicated verbose logs are added for both min and max bound check failures to have diagnostics consistent with variable offset handling in check_map_access(). [1] https://marc.info/?l=linux-netdev&m=155433357510597&w=2 Fixes: 2011fccfb61b ("bpf: Support variable offset stack access from helpers") Reported-by: Daniel Borkmann Signed-off-by: Andrey Ignatov --- kernel/bpf/verifier.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f26a64f55712..b7e1be8ccc51 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2248,16 +2248,28 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno, if (meta && meta->raw_mode) meta = NULL; + if (reg->smax_value >= BPF_MAX_VAR_OFF || + reg->smax_value <= -BPF_MAX_VAR_OFF) { + verbose(env, "R%d unbounded indirect variable offset stack access\n", + regno); + return -EACCES; + } min_off = reg->smin_value + reg->off; - max_off = reg->umax_value + reg->off; + max_off = reg->smax_value + reg->off; err = __check_stack_boundary(env, regno, min_off, access_size, zero_size_allowed); - if (err) + if (err) { + verbose(env, "R%d min value is outside of stack bound\n", + regno); return err; + } err = __check_stack_boundary(env, regno, max_off, access_size, zero_size_allowed); - if (err) + if (err) { + verbose(env, "R%d max value is outside of stack bound\n", + regno); return err; + } } if (meta && meta->raw_mode) {