Commit 95a762e2 authored Dec 18, 2017 by Jann Horn Committed by Daniel Borkmann Dec 21, 2017

bpf: fix incorrect sign extension in check_alu_op()



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: 48461135 ("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>

parent 4374f256

kernel/bpf/verifier.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -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) {