Merge branch 'relax-allowlist-for-open-coded-css_task-iter'

Chuyi Zhou says:

====================
Relax allowlist for open-coded css_task iter

Hi,
The patchset aims to relax the allowlist for open-coded css_task iter
suggested by Alexei[1].

Please see individual patches for more details. And comments are always
welcome.

Patch summary:
 * Patch #1: Relax the allowlist and let css_task iter can be used in
   bpf iters and any sleepable progs.
 * Patch #2: Add a test in cgroup_iters.c which demonstrates how
   css_task iters can be combined with cgroup iter.
 * Patch #3: Add a test to prove css_task iter can be used in normal
 * sleepable progs.
link[1]:https://lore.kernel.org/lkml/CAADnVQKafk_junRyE=-FVAik4hjTRDtThymYGEL8hGTuYoOGpA@mail.gmail.com/
---

Changes in v2:
 * Fix the incorrect logic in check_css_task_iter_allowlist. Use
   expected_attach_type to check whether we are using bpf_iters.
 * Link to v1:https://lore.kernel.org/bpf/20231022154527.229117-1-zhouchuyi@bytedance.com/T/#m946f9cde86b44a13265d9a44c5738a711eb578fd
Changes in v3:
 * Add a testcase to prove css_task can be used in fentry.s
 * Link to v2:https://lore.kernel.org/bpf/20231024024240.42790-1-zhouchuyi@bytedance.com/T/#m14a97041ff56c2df21bc0149449abd275b73f6a3
Changes in v4:
 * Add Yonghong's ack for patch #1 and patch #2.
 * Solve Yonghong's comments for patch #2
 * Move prog 'iter_css_task_for_each_sleep' from iters_task_failure.c to
   iters_css_task.c. Use RUN_TESTS to prove we can load this prog.
 * Link to v3:https://lore.kernel.org/bpf/20231025075914.30979-1-zhouchuyi@bytedance.com/T/#m3200d8ad29af4ffab97588e297361d0a45d7585d

---
====================

Link: https://lore.kernel.org/r/20231031050438.93297-1-zhouchuyi@bytedance.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 12 insertions, 4 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 014b4d1ef408..def99b1a2b17 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11402,6 +11402,12 @@ static int process_kf_arg_ptr_to_rbtree_node(struct bpf_verifier_env *env,
 						  &meta->arg_rbtree_root.field);
 }
 
+/*
+ * css_task iter allowlist is needed to avoid dead locking on css_set_lock.
+ * LSM hooks and iters (both sleepable and non-sleepable) are safe.
+ * Any sleepable progs are also safe since bpf_check_attach_target() enforce
+ * them can only be attached to some specific hook points.
+ */
 static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
@@ -11409,10 +11415,12 @@ static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
 	switch (prog_type) {
 	case BPF_PROG_TYPE_LSM:
 		return true;
-	case BPF_TRACE_ITER:
-		return env->prog->aux->sleepable;
+	case BPF_PROG_TYPE_TRACING:
+		if (env->prog->expected_attach_type == BPF_TRACE_ITER)
+			return true;
+		fallthrough;
 	default:
-		return false;
+		return env->prog->aux->sleepable;
 	}
 }
 
@@ -11671,7 +11679,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_ITER:
 			if (meta->func_id == special_kfunc_list[KF_bpf_iter_css_task_new]) {
 				if (!check_css_task_iter_allowlist(env)) {
-					verbose(env, "css_task_iter is only allowed in bpf_lsm and bpf iter-s\n");
+					verbose(env, "css_task_iter is only allowed in bpf_lsm, bpf_iter and sleepable progs\n");
 					return -EINVAL;
 				}
 			}