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 09DE4C282CD for ; Mon, 28 Jan 2019 20:23:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DB1B42183F for ; Mon, 28 Jan 2019 20:23:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727252AbfA1UXl (ORCPT ); Mon, 28 Jan 2019 15:23:41 -0500 Received: from www62.your-server.de ([213.133.104.62]:44694 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726859AbfA1UXk (ORCPT ); Mon, 28 Jan 2019 15:23:40 -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 1goDRT-0003ZD-8N; Mon, 28 Jan 2019 21:23:39 +0100 From: Daniel Borkmann To: gregkh@linuxfoundation.org Cc: ast@kernel.org, stable@vger.kernel.org, Daniel Borkmann Subject: [PATCH stable 4.20 05/10] bpf: restrict stack pointer arithmetic for unprivileged Date: Mon, 28 Jan 2019 21:23:25 +0100 Message-Id: <20190128202330.32664-6-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 e4298d25830a866cc0f427d4bccb858e76715859 upstream ] Restrict stack pointer arithmetic for unprivileged users in that arithmetic itself must not go out of bounds as opposed to the actual access later on. Therefore after each adjust_ptr_min_max_vals() with a stack pointer as a destination we simulate a check_stack_access() of 1 byte on the destination and once that fails the program is rejected for unprivileged program loads. This is analog to map value pointer arithmetic and needed for masking later on. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 63 ++++++++++++++++++++++++++++--------------- 1 file changed, 41 insertions(+), 22 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 517ac90f9e01..288f045cb6a6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1314,6 +1314,31 @@ static int check_stack_read(struct bpf_verifier_env *env, } } +static int check_stack_access(struct bpf_verifier_env *env, + const struct bpf_reg_state *reg, + int off, int size) +{ + /* Stack accesses must be at a fixed offset, so that we + * can determine what type of data were returned. See + * check_stack_read(). + */ + if (!tnum_is_const(reg->var_off)) { + char tn_buf[48]; + + tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off); + verbose(env, "variable stack access var_off=%s off=%d size=%d", + tn_buf, off, size); + return -EACCES; + } + + if (off >= 0 || off < -MAX_BPF_STACK) { + verbose(env, "invalid stack off=%d size=%d\n", off, size); + return -EACCES; + } + + return 0; +} + /* check read/write into map element returned by bpf_map_lookup_elem() */ static int __check_map_access(struct bpf_verifier_env *env, u32 regno, int off, int size, bool zero_size_allowed) @@ -1870,24 +1895,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn } } else if (reg->type == PTR_TO_STACK) { - /* stack accesses must be at a fixed offset, so that we can - * determine what type of data were returned. - * See check_stack_read(). - */ - if (!tnum_is_const(reg->var_off)) { - char tn_buf[48]; - - tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off); - verbose(env, "variable stack access var_off=%s off=%d size=%d", - tn_buf, off, size); - return -EACCES; - } off += reg->var_off.value; - if (off >= 0 || off < -MAX_BPF_STACK) { - verbose(env, "invalid stack off=%d size=%d\n", off, - size); - return -EACCES; - } + err = check_stack_access(env, reg, off, size); + if (err) + return err; state = func(env, reg); err = update_stack_depth(env, state, off); @@ -3169,11 +3180,19 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, /* For unprivileged we require that resulting offset must be in bounds * in order to be able to sanitize access later on. */ - if (!env->allow_ptr_leaks && dst_reg->type == PTR_TO_MAP_VALUE && - check_map_access(env, dst, dst_reg->off, 1, false)) { - verbose(env, "R%d pointer arithmetic of map value goes out of range, prohibited for !root\n", - dst); - return -EACCES; + if (!env->allow_ptr_leaks) { + if (dst_reg->type == PTR_TO_MAP_VALUE && + check_map_access(env, dst, dst_reg->off, 1, false)) { + verbose(env, "R%d pointer arithmetic of map value goes out of range, " + "prohibited for !root\n", dst); + return -EACCES; + } else if (dst_reg->type == PTR_TO_STACK && + check_stack_access(env, dst_reg, dst_reg->off + + dst_reg->var_off.value, 1)) { + verbose(env, "R%d stack pointer arithmetic goes out of range, " + "prohibited for !root\n", dst); + return -EACCES; + } } return 0; -- 2.17.1