Re: Bug with BPF_ALU64 | BPF_END?

[Daniel Borkmann]

On 09/14/2017 07:53 PM, Edward Cree wrote:

Is BPF_END supposed to only be used with BPF_ALU, never with BPF_ALU64?
In kernel/bpf/core.c:___bpf_prog_run(), there are only jump table targets
  for the BPF_ALU case, not for the BPF_ALU64 case (opcodes 0xd7 and 0xdf).
But the verifier doesn't enforce this; by crafting a program that uses
  these opcodes I can get a WARN when they're run (without JIT; it looks
  like the x86 JIT, at least, won't like it either).
Proposed patch below the cut; build-tested only.

-Ed
---

[PATCH net] bpf/verifier: reject BPF_ALU64|BPF_END

Neither ___bpf_prog_run nor the JITs accept it.

Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)")
Signed-off-by: Edward Cree <ec...@solarflare.com>

Good catch! Can you submit this as an official patch for -net together
with a test case for tools/testing/selftests/bpf/test_verifier.c?

Thanks!

Acked-by: Daniel Borkmann <dan...@iogearbox.net>

---
  kernel/bpf/verifier.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 477b693..799b245 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2292,7 +2292,8 @@ static int check_alu_op(struct bpf_verifier_env *env, 
struct bpf_insn *insn)
                        }
                } else {
                        if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
-                           (insn->imm != 16 && insn->imm != 32 && insn->imm != 
64)) {
+                           (insn->imm != 16 && insn->imm != 32 && insn->imm != 
64) ||
+                           BPF_CLASS(insn->code) == BPF_ALU64) {
                                verbose("BPF_END uses reserved fields\n");
                                return -EINVAL;
                        }