From: Jiri Olsa <olsajiri@xxxxxxxxx> syzbot reported an verifier bug [1] where the helper func pointer could be NULL due to disabled config option. As Alexei suggested we could check on that in get_helper_proto directly. Excluding tail_call helper from the check, because it is NULL by design and valid in all configs. [1] https://lore.kernel.org/bpf/68904050.050a0220.7f033.0001.GAE@xxxxxxxxxx/ Reported-by: syzbot+a9ed3d9132939852d0df@xxxxxxxxxxxxxxxxxxxxxxxxx Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> --- v2 changes: - set bpf_tail_call_proto.func to -1 so we can skip the extra check [Andrii] kernel/bpf/core.c | 5 ++++- kernel/bpf/verifier.c | 2 +- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 5d1650af899d..0f6e9a3d9960 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -3024,7 +3024,10 @@ EXPORT_SYMBOL_GPL(bpf_event_output); /* Always built-in helper functions. */ const struct bpf_func_proto bpf_tail_call_proto = { - .func = NULL, + /* func is unused for tail_call, we set it to pass the + * get_helper_proto check + */ + .func = (void *) 1, .gpl_only = false, .ret_type = RET_VOID, .arg1_type = ARG_PTR_TO_CTX, diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index c4f69a9e9af6..c89e2b1bc644 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11354,7 +11354,7 @@ static int get_helper_proto(struct bpf_verifier_env *env, int func_id, return -EINVAL; *ptr = env->ops->get_func_proto(func_id, env->prog); - return *ptr ? 0 : -EINVAL; + return *ptr && (*ptr)->func ? 0 : -EINVAL; } static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn, -- 2.50.1
