selftests/bpf: Use memcpy() for bounded non-NULL-terminated copies

Replace strncpy() with memcpy() in cases where the source is
non-NULL-terminated and the copy length is known.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260223190736.649171-6-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: theihor

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

@@ -308,8 +308,10 @@ static int find_field_offset(struct btf *btf, char *pattern, regmatch_t *matches
 		return -1;
 	}
 
-	strncpy(type_str, type, type_sz);
-	strncpy(field_str, field, field_sz);
+	memcpy(type_str, type, type_sz);
+	type_str[type_sz] = '\0';
+	memcpy(field_str, field, field_sz);
+	field_str[field_sz] = '\0';
 	btf_id = btf__find_by_name(btf, type_str);
 	if (btf_id < 0) {
 		PRINT_FAIL("No BTF info for type %s\n", type_str);

tools/testing/selftests/bpf/test_verifier.c

@@ -1320,7 +1320,7 @@ static bool cmp_str_seq(const char *log, const char *exp)
 			printf("FAIL\nTestcase bug\n");
 			return false;
 		}
-		strncpy(needle, exp, len);
+		memcpy(needle, exp, len);
 		needle[len] = 0;
 		q = strstr(log, needle);
 		if (!q) {