From 6e12ea4fb45ca86cdd7425276b6993455fee947a Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Fri, 22 Dec 2017 16:23:05 +0100 Subject: [PATCH] bpf: fix incorrect sign extension in check_alu_op() From: Jann Horn [ 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) CVE: CVE-2017-16995 Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=6e12ea4fb45ca86cdd7425276b6993455fee947a] 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 Signed-off-by: Greg Kroah-Hartman Signed-off-by: Andreas Wellving --- 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 c6ec04f94525..2811ced3c2a9 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2374,7 +2374,13 @@ 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) { -- 2.20.1