[PATCH bpf] bpf: Fix program BTF use-after-free in sleepable programs

[Sanghyun Park <sanghyun.park.cnu@gmail.com>]

Object kfunc calls embed metadata owned by the program BTF. A sleepable
program can remain active under Tasks Trace RCU after its last reference is
dropped, while program teardown releases the BTF through ordinary RCU. The
invocation can then dereference freed metadata in bpf_obj_new().

Move btf_put() into __bpf_prog_put_rcu(), the callback that frees the
program. When teardown is deferred, that callback runs after the program's
own grace period (Tasks Trace RCU for sleepable programs and ordinary RCU
otherwise), so the BTF outlives every active invocation. The non-deferred
path invokes the callback synchronously, so load-error cleanup stays direct.

Fixes: 958cf2e273f0 ("bpf: Introduce bpf_obj_new")
Signed-off-by: Sanghyun Park <sanghyun.park.cnu@gmail.com>
---
 kernel/bpf/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6db306d23b479f..3b6cf93c43c4d6 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2438,6 +2438,7 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu)
 {
 	struct bpf_prog_aux *aux = container_of(rcu, struct bpf_prog_aux, rcu);
 
+	btf_put(aux->btf);
 	kvfree(aux->func_info);
 	kfree(aux->func_info_aux);
 	free_uid(aux->user);
@@ -2448,7 +2449,6 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu)
 static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
 {
 	bpf_prog_kallsyms_del_all(prog);
-	btf_put(prog->aux->btf);
 	module_put(prog->aux->mod);
 	kvfree(prog->aux->jited_linfo);
 	kvfree(prog->aux->linfo);
-- 
2.48.1