[PATCH bpf v1 06/10] selftests/bpf: Reject resilient unlock in rbtree callback

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add a load-only verifier regression for a resilient lock operation in an
rbtree comparison callback. The program holds the rbtree's regular spin
lock and a separate resilient lock, then releases the resilient lock from
the callback. This isolates the missing kfunc policy check without running
a concurrent tree mutation.

Release the resilient lock before the regular lock on the outer
fall-through. The broken verifier therefore accepts the balanced program,
while the fixed verifier rejects the resilient unlock specifically while
verifying the callback.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../testing/selftests/bpf/progs/rbtree_fail.c | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/rbtree_fail.c b/tools/testing/selftests/bpf/progs/rbtree_fail.c
index 555379952dcc..803419a47c62 100644
--- a/tools/testing/selftests/bpf/progs/rbtree_fail.c
+++ b/tools/testing/selftests/bpf/progs/rbtree_fail.c
@@ -16,6 +16,7 @@ struct node_data {
 private(A) struct bpf_spin_lock glock;
 private(A) struct bpf_rb_root groot __contains(node_data, node);
 private(A) struct bpf_rb_root groot2 __contains(node_data, node);
+private(B) struct bpf_res_spin_lock res_glock;
 
 static bool less(struct bpf_rb_node *a, const struct bpf_rb_node *b)
 {
@@ -265,6 +266,12 @@ static bool less__bad_fn_call_first_unlock_after(struct bpf_rb_node *a, const st
 	return node_a->key < node_b->key;
 }
 
+static bool less__bad_res_spin_unlock(struct bpf_rb_node *a, const struct bpf_rb_node *b)
+{
+	bpf_res_spin_unlock(&res_glock);
+	return false;
+}
+
 static __always_inline
 long add_with_cb(bool (cb)(struct bpf_rb_node *a, const struct bpf_rb_node *b))
 {
@@ -301,4 +308,26 @@ long rbtree_api_add_bad_cb_bad_fn_call_first_unlock_after(void *ctx)
 	return add_with_cb(less__bad_fn_call_first_unlock_after);
 }
 
+SEC("?tc")
+__failure __msg("can't res_spin_{lock,unlock} in rbtree cb")
+long rbtree_api_add_bad_cb_res_spin_unlock(void *ctx)
+{
+	struct node_data *n;
+
+	n = bpf_obj_new(typeof(*n));
+	if (!n)
+		return 1;
+
+	bpf_spin_lock(&glock);
+	if (bpf_res_spin_lock(&res_glock)) {
+		bpf_spin_unlock(&glock);
+		bpf_obj_drop(n);
+		return 1;
+	}
+	bpf_rbtree_add(&groot, &n->node, less__bad_res_spin_unlock);
+	bpf_res_spin_unlock(&res_glock);
+	bpf_spin_unlock(&glock);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.53.0