Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d75d3ee2 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by Greg Kroah-Hartman
Browse files

bpf: reject out-of-bounds stack pointer calculation 




From: Jann Horn <jannh@google.com>

Reject programs that compute wildly out-of-bounds stack pointers.
Otherwise, pointers can be computed with an offset that doesn't fit into an
`int`, causing security issues in the stack memory access check (as well as
signed integer overflow during offset addition).

This is a fix specifically for the v4.9 stable tree because the mainline
code looks very different at this point.

Fixes: 7bca0a97 ("bpf: enhance verifier to understand stack pointer arithmetic")
Signed-off-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 7b5b73ea

kernel/bpf/verifier.c

+20 −2
Original line number Diff line number Diff line
@@ -1861,10 +1861,28 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) 
			   ((BPF_SRC(insn->code) == BPF_X &&

			     regs[insn->src_reg].type == CONST_IMM) ||

			    BPF_SRC(insn->code) == BPF_K)) {

			if (BPF_SRC(insn->code) == BPF_X)

			if (BPF_SRC(insn->code) == BPF_X) {

				/* check in case the register contains a big

				 * 64-bit value

				 */

				if (regs[insn->src_reg].imm < -MAX_BPF_STACK ||

				    regs[insn->src_reg].imm > MAX_BPF_STACK) {

					verbose("R%d value too big in R%d pointer arithmetic\n",

						insn->src_reg, insn->dst_reg);

					return -EACCES;

				}

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

			else

			} else {

				/* safe against overflow: addition of 32-bit

				 * numbers in 64-bit representation

				 */

				dst_reg->imm += insn->imm;

			}

			if (dst_reg->imm > 0 || dst_reg->imm < -MAX_BPF_STACK) {

				verbose("R%d out-of-bounds pointer arithmetic\n",

					insn->dst_reg);

				return -EACCES;

			}

			return 0;

		} else if (opcode == BPF_ADD &&

			   BPF_CLASS(insn->code) == BPF_ALU64 &&