bpf: Check attach_func_proto more carefully in check_helper_call

Syzkaller found a problem similar to d1a6edecc1fd ("bpf: Check
attach_func_proto more carefully in check_return_code") where
attach_func_proto might be NULL:

RIP: 0010:check_helper_call+0x3dcb/0x8d50 kernel/bpf/verifier.c:7330
 do_check kernel/bpf/verifier.c:12302 [inline]
 do_check_common+0x6e1e/0xb980 kernel/bpf/verifier.c:14610
 do_check_main kernel/bpf/verifier.c:14673 [inline]
 bpf_check+0x661e/0xc520 kernel/bpf/verifier.c:15243
 bpf_prog_load+0x11ae/0x1f80 kernel/bpf/syscall.c:2620

With the following reproducer:

  bpf$BPF_PROG_RAW_TRACEPOINT_LOAD(0x5, &(0x7f0000000780)={0xf, 0x4, &(0x7f0000000040)=@framed={{}, [@call={0x85, 0x0, 0x0, 0xbb}]}, &(0x7f0000000000)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0, 0x2b, 0xffffffffffffffff, 0x8, 0x0, 0x0, 0x10, 0x0}, 0x80)

Let's do the same here, only check attach_func_proto for the prog types
where we are certain that attach_func_proto is defined.

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Reported-by: syzbot+0f8d989b1fba1addc5e0@syzkaller.appspotmail.com
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220720164729.147544-1-sdf@google.com

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c59c3df..7c1e056 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7170,6 +7170,7 @@ static void update_loop_inline_state(struct bpf_verifier_env *env, u32 subprogno
 static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
                             int *insn_idx_p)
 {
+       enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
        const struct bpf_func_proto *fn = NULL;
        enum bpf_return_type ret_type;
        enum bpf_type_flag ret_flag;
@@ -7331,7 +7332,8 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
                }
                break;
        case BPF_FUNC_set_retval:
-               if (env->prog->expected_attach_type == BPF_LSM_CGROUP) {
+               if (prog_type == BPF_PROG_TYPE_LSM &&
+                   env->prog->expected_attach_type == BPF_LSM_CGROUP) {
                        if (!env->prog->aux->attach_func_proto->type) {
                                /* Make sure programs that attach to void
                                 * hooks don't try to modify return value.