| From foo@baz Fri Dec 22 16:57:35 CET 2017 |
| From: Daniel Borkmann <daniel@iogearbox.net> |
| Date: Fri, 22 Dec 2017 16:29:04 +0100 |
| Subject: bpf: reject out-of-bounds stack pointer calculation |
| To: gregkh@linuxfoundation.org |
| Cc: ast@kernel.org, daniel@iogearbox.net, jannh@google.com, stable@vger.kernel.org |
| Message-ID: <20171222152905.3455-4-daniel@iogearbox.net> |
| |
| From: Daniel Borkmann <daniel@iogearbox.net> |
| |
| |
| 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: 7bca0a9702edf ("bpf: enhance verifier to understand stack pointer arithmetic") |
| Signed-off-by: Jann Horn <jannh@google.com> |
| Acked-by: Daniel Borkmann <daniel@iogearbox.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/bpf/verifier.c | 22 ++++++++++++++++++++-- |
| 1 file changed, 20 insertions(+), 2 deletions(-) |
| |
| --- a/kernel/bpf/verifier.c |
| +++ b/kernel/bpf/verifier.c |
| @@ -1861,10 +1861,28 @@ static int check_alu_op(struct bpf_verif |
| ((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 && |