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Commit 3695b3b1 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Greg Kroah-Hartman
Browse files

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: 48461135 ("bpf: allow access into map value arrays")
Signed-off-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarEdward Cree <ecree@solarflare.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d75d3ee2

kernel/bpf/verifier.c

+10 −3
Original line number Diff line number Diff line
@@ -1790,10 +1790,17 @@ 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].max_value = insn->imm;

			regs[insn->dst_reg].min_value = insn->imm;

			regs[insn->dst_reg].imm = imm;

			regs[insn->dst_reg].max_value = imm;

			regs[insn->dst_reg].min_value = imm;

		}



	} else if (opcode > BPF_END) {