[PATCH bpf v2] bpf,lsm: drop bpf_prog_free from sleepable_lsm_hooks

[Sechang Lim]

__bpf_prog_put_rcu() is the call_rcu() callback for non-sleepable programs.
security_bpf_prog_free() called from there fires bpf_prog_free in softirq;
if a sleepable LSM prog is attached to that hook, might_fault() BUGs:

  BUG: sleeping function called from invalid context
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 5038
  preempt_count: 101, expected: 0
  Call Trace:
   <IRQ>
   __bpf_prog_enter_sleepable+0x1cd/0x320 kernel/bpf/trampoline.c:1255
   bpf_trampoline_6442549705+0x53/0xd7
   security_bpf_prog_free+0xde/0x130 security/security.c:5465
   __bpf_prog_put_rcu+0xab/0xd0 kernel/bpf/syscall.c:2365
   rcu_do_batch kernel/rcu/tree.c:2617 [inline]
   handle_softirqs+0x236/0x800 kernel/softirq.c:622
   </IRQ>

The call_rcu/call_rcu_tasks_trace split reflects the freed program's
sleepability, not that of any attached observer.

security_bpf_prog_free() also frees prog->aux->security, which has to stay
after the grace period, so drop bpf_prog_free from sleepable_lsm_hooks
rather than move the call. Non-sleepable observers still run there.

Fixes: 1b67772e4e3f ("bpf,lsm: Refactor bpf_prog_alloc/bpf_prog_free LSM hooks")
Signed-off-by: Sechang Lim <rhkrqnwk98@xxxxxxxxx>
---
v2:
 - remove security_bpf_prog_free from sleepable (Alexei Starovoitov)

v1:
 - https://lore.kernel.org/all/20260626093711.2969648-1-rhkrqnwk98@xxxxxxxxx/

 kernel/bpf/bpf_lsm.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index c5c925f00202..d2dd5a1b557d 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -292,7 +292,6 @@ BTF_ID(func, bpf_lsm_bpf_map_create)
 BTF_ID(func, bpf_lsm_bpf_map_free)
 BTF_ID(func, bpf_lsm_bpf_prog)
 BTF_ID(func, bpf_lsm_bpf_prog_load)
-BTF_ID(func, bpf_lsm_bpf_prog_free)
 BTF_ID(func, bpf_lsm_bpf_token_create)
 BTF_ID(func, bpf_lsm_bpf_token_free)
 BTF_ID(func, bpf_lsm_bpf_token_cmd)
-- 
2.43.0