From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Thu, 4 Jan 2018 08:01:22 -0600 Subject: [PATCH] bpf: fix incorrect sign extension in check_alu_op() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ Upstream commit 95a762e2c8c942780948091f8f2a4f32fce1ac6f ] 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 Signed-off-by: Daniel Borkmann CVE-2017-16995 Signed-off-by: Seth Forshee Signed-off-by: Andy Whitcroft Signed-off-by: Kleber Sacilotto de Souza (cherry picked from commit 868c88129c7567525dbde3cb6989a5acd478bd80) Signed-off-by: Fabian Grünbichler --- kernel/bpf/verifier.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 4321625fe32a..cdfa07a4ef27 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2048,12 +2048,19 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) /* case: R = imm * remember the value we stored into this reg */ + u64 imm; + + if (BPF_CLASS(insn->code) == BPF_ALU64) + imm = insn->imm; + else + imm = (u32)insn->imm; + regs[insn->dst_reg].type = CONST_IMM; - regs[insn->dst_reg].imm = insn->imm; + regs[insn->dst_reg].imm = imm; regs[insn->dst_reg].id = 0; - regs[insn->dst_reg].max_value = insn->imm; - regs[insn->dst_reg].min_value = insn->imm; - regs[insn->dst_reg].min_align = calc_align(insn->imm); + regs[insn->dst_reg].max_value = imm; + regs[insn->dst_reg].min_value = imm; + regs[insn->dst_reg].min_align = calc_align(imm); regs[insn->dst_reg].value_from_signed = false; } -- 2.14.2