diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2017-12-22 16:29:04 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-12-25 14:23:47 +0100 |
| commit | d75d3ee237cee9068022117e059b64bbab617f3d (patch) | |
| tree | 787369e2a9360b16329b5fcee3007ab063003155 /kernel | |
| parent | 7b5b73ea87a06236fa124bdebed1390d362d3439 (diff) | |
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: 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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2f19c94452dd..b03af36b8e87 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -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 && |