[PATCH bpf-next v1 2/2] selftests/bpf: Add test for bpf_obj_drop with bad reg->off

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

Add a selftest for the fix provided in the previous commit. Without the
fix, the selftest passes the verifier while it should fail. The special
logic for detecting graph root or node for reg->off and bypassing
reg->off == 0 guarantee for release helpers/kfuncs has been dropped.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../bpf/progs/local_kptr_stash_fail.c         | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c b/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c
index 5484d1e9801d..fcf7a7567da2 100644
--- a/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c
+++ b/tools/testing/selftests/bpf/progs/local_kptr_stash_fail.c
@@ -62,4 +62,24 @@ long stash_rb_nodes(void *ctx)
 	return 0;
 }
 
+SEC("tc")
+__failure __msg("R1 must have zero offset when passed to release func")
+long drop_rb_node_off(void *ctx)
+{
+	struct map_value *mapval;
+	struct node_data *res;
+	int idx = 0;
+
+	mapval = bpf_map_lookup_elem(&some_nodes, &idx);
+	if (!mapval)
+		return 1;
+
+	res = bpf_obj_new(typeof(*res));
+	if (!res)
+		return 1;
+	/* Try releasing with graph node offset */
+	bpf_obj_drop(&res->node);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.41.0