[replying to both of your messages here] On Wed, Feb 21, 2024 at 3:59 AM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Fri, Feb 16, 2024 at 10:50:10AM +0100, Benjamin Tissoires wrote: > > static bool is_rbtree_lock_required_kfunc(u32 btf_id) > > { > > return is_bpf_rbtree_api_kfunc(btf_id); > > @@ -12140,6 +12143,16 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn, > > } > > } > > > > + if (is_bpf_timer_set_sleepable_cb_kfunc(meta.func_id)) { > > + err = push_callback_call(env, insn, insn_idx, meta.subprogno, > > + set_timer_callback_state); > > + if (err) { > > + verbose(env, "kfunc %s#%d failed callback verification\n", > > + func_name, meta.func_id); > > + return err; > > + } > > + } > > All makes sense so far. > Please squash all the fix and repost. > It's hard to do a proper review in this shape of the patch. Yeah, I was expecting a very quick "I know why you are crashing", not a full review here. > As far as rcu_read_lock/unlock that is done in callback... > it feels buggy and unnecessary. This rcu approach is indeed wrong, but there still needs to be some locking if bpf_timer_set_callback() or bpf_timer_set_sleepable_cb() is called while the work just started. I went with a semaphore in v3 as it seemed lightweight enough there. Please shout if you disagree :) Anyway, I've also dropped the flags in bpf_timer_init() in v3 to only add BPF_F_TIMER_SLEEPABLE in bpf_timer_start(). V3 (not RFC) is coming. Cheers, Benjamin > bpf prog and timer won't disappear while work is queued. > array and hash map will call bpf_obj_free_timer() before going away. > > And things like: > + rcu_read_lock(); > + callback_fn = rcu_dereference(t->sleepable_cb_fn); > + rcu_read_unlock(); > + if (!callback_fn) > + return; > > is 99% broken. if (!callback_fn) line is UAF. >