From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH bpf 2/9] bpf: fix incorrect sign extension in check_alu_op() Date: Mon, 18 Dec 2017 20:11:54 -0800 Message-ID: <20171219041201.1979983-3-ast@kernel.org> References: <20171219041201.1979983-1-ast@kernel.org> Mime-Version: 1.0 Content-Type: text/plain Cc: Daniel Borkmann , Jann Horn , Edward Cree , , To: "David S . Miller" Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:50652 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937387AbdLSEME (ORCPT ); Mon, 18 Dec 2017 23:12:04 -0500 Received: from pps.filterd (m0109332.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBJ494JH027071 for ; Mon, 18 Dec 2017 20:12:04 -0800 Received: from mail.thefacebook.com ([199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 2exqrvgf3w-3 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Mon, 18 Dec 2017 20:12:04 -0800 In-Reply-To: <20171219041201.1979983-1-ast@kernel.org> Sender: netdev-owner@vger.kernel.org List-ID: From: Jann Horn Distinguish between BPF_ALU64|BPF_MOV|BPF_K (load 32-bit immediate, sign-extended to 64-bit) and BPF_ALU|BPF_MOV|BPF_K (load 32-bit immediate, zero-padded to 64-bit); only perform sign extension in the first case. Starting with v4.14, this is exploitable by unprivileged users as long as the unprivileged_bpf_disabled sysctl isn't set. Debian assigned CVE-2017-16995 for this issue. v3: - add CVE number (Ben Hutchings) Fixes: 484611357c19 ("bpf: allow access into map value arrays") Signed-off-by: Jann Horn Acked-by: Edward Cree Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 625e358ca765..c086010ae51e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2408,7 +2408,13 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) * remember the value we stored into this reg */ regs[insn->dst_reg].type = SCALAR_VALUE; - __mark_reg_known(regs + insn->dst_reg, insn->imm); + if (BPF_CLASS(insn->code) == BPF_ALU64) { + __mark_reg_known(regs + insn->dst_reg, + insn->imm); + } else { + __mark_reg_known(regs + insn->dst_reg, + (u32)insn->imm); + } } } else if (opcode > BPF_END) { -- 2.9.5