selftests/bpf: Fix out-of-bounds array access bugs reported by ASAN

- kmem_cache_iter: remove unnecessary debug output
- lwt_seg6local: change the type of foobar to char[]
  - the sizeof(foobar) returned the pointer size and not a string
    length as intended
- verifier_log: increase prog_name buffer size in verif_log_subtest()
  - compiler has a conservative estimate of fixed_log_sz value, making
    ASAN complain on snprint() call

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260223191118.655185-1-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/kmem_cache_iter.c

@@ -104,11 +104,8 @@ void test_kmem_cache_iter(void)
 	if (!ASSERT_GE(iter_fd, 0, "iter_create"))
 		goto destroy;
 
-	memset(buf, 0, sizeof(buf));
-	while (read(iter_fd, buf, sizeof(buf)) > 0) {
-		/* Read out all contents */
-		printf("%s", buf);
-	}
+	while (read(iter_fd, buf, sizeof(buf)) > 0)
+		; /* Read out all contents */
 
 	/* Next reads should return 0 */
 	ASSERT_EQ(read(iter_fd, buf, sizeof(buf)), 0, "read");

tools/testing/selftests/bpf/prog_tests/lwt_seg6local.c

@@ -117,7 +117,7 @@ void test_lwt_seg6local(void)
 	const char *ns1 = NETNS_BASE "1";
 	const char *ns6 = NETNS_BASE "6";
 	struct nstoken *nstoken = NULL;
-	const char *foobar = "foobar";
+	const char foobar[] = "foobar";
 	ssize_t bytes;
 	int sfd, cfd;
 	char buf[7];

tools/testing/selftests/bpf/prog_tests/verifier_log.c

@@ -47,7 +47,7 @@ static int load_prog(struct bpf_prog_load_opts *opts, bool expect_load_error)
 static void verif_log_subtest(const char *name, bool expect_load_error, int log_level)
 {
 	LIBBPF_OPTS(bpf_prog_load_opts, opts);
-	char *exp_log, prog_name[16], op_name[32];
+	char *exp_log, prog_name[24], op_name[32];
 	struct test_log_buf *skel;
 	struct bpf_program *prog;
 	size_t fixed_log_sz;