From: Daniel Borkmann <daniel@iogearbox.net>
Date: Fri, 22 Dec 2017 15:23:05 +0000 (+0100)
Subject: bpf: fix incorrect sign extension in check_alu_op()
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=6e12ea4fb45ca86cdd7425276b6993455fee947a;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

bpf: fix incorrect sign extension in check_alu_op()


From: Jann Horn <jannh@google.com>

[ 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 <jannh@google.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

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) {