On Wed, Aug 13, 2025 at 03:44:43PM -0700, Andrii Nakryiko wrote: > On Wed, Aug 13, 2025 at 6:38 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > 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, > > we seem to have BPF_PTR_POISON in include/linux/poison.h, let's use > that instead of 1? ah I did not know about this macro, thanks jirka > > pw-bot: cr > > > > .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 > >
