[PATCH bpf-next v1 5/6] bpf: selftests: Fix fd cleanup in sk_lookup test

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

Similar to the fix in commit:
e31eec77e4ab (bpf: selftests: Fix fd cleanup in get_branch_snapshot)

We use memset to set fds to -1 without breaking on future changes to
the array size (when MAX_SERVER constant is bumped).

The particular close(0) occurs on non-reuseport tests, so it can be seen
with -n 115/{2,3} but not 115/4. This can cause problems with future
tests if they depend on BTF fd never being acquired as fd 0, breaking
internal libbpf assumptions.

Cc: Jakub Sitnicki <jakub@cloudflare.com>
Fixes: 0ab5539f8584 (selftests/bpf: Tests for BPF_SK_LOOKUP attach point)
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/prog_tests/sk_lookup.c      | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
index aee41547e7f4..572220065bdf 100644
--- a/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
+++ b/tools/testing/selftests/bpf/prog_tests/sk_lookup.c
@@ -598,11 +598,14 @@ static void query_lookup_prog(struct test_sk_lookup *skel)
 
 static void run_lookup_prog(const struct test *t)
 {
-	int server_fds[MAX_SERVERS] = { -1 };
 	int client_fd, reuse_conn_fd = -1;
 	struct bpf_link *lookup_link;
+	int server_fds[MAX_SERVERS];
 	int i, err;
 
+	/* set all fds to -1 */
+	memset(server_fds, 0xFF, sizeof(server_fds));
+
 	lookup_link = attach_lookup_prog(t->lookup_prog);
 	if (!lookup_link)
 		return;
@@ -663,8 +666,9 @@ static void run_lookup_prog(const struct test *t)
 	if (reuse_conn_fd != -1)
 		close(reuse_conn_fd);
 	for (i = 0; i < ARRAY_SIZE(server_fds); i++) {
-		if (server_fds[i] != -1)
-			close(server_fds[i]);
+		if (server_fds[i] == -1)
+			break;
+		close(server_fds[i]);
 	}
 	bpf_link__destroy(lookup_link);
 }
@@ -1053,11 +1057,14 @@ static void run_sk_assign(struct test_sk_lookup *skel,
 			  struct bpf_program *lookup_prog,
 			  const char *remote_ip, const char *local_ip)
 {
-	int server_fds[MAX_SERVERS] = { -1 };
+	int server_fds[MAX_SERVERS];
 	struct bpf_sk_lookup ctx;
 	__u64 server_cookie;
 	int i, err;
 
+	/* set all fds to -1 */
+	memset(server_fds, 0xFF, sizeof(server_fds));
+
 	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
 		.ctx_in = &ctx,
 		.ctx_size_in = sizeof(ctx),
@@ -1097,8 +1104,9 @@ static void run_sk_assign(struct test_sk_lookup *skel,
 
 close_servers:
 	for (i = 0; i < ARRAY_SIZE(server_fds); i++) {
-		if (server_fds[i] != -1)
-			close(server_fds[i]);
+		if (server_fds[i] == -1)
+			break;
+		close(server_fds[i]);
 	}
 }
 
-- 
2.33.0