selftest/bpf: Testing for multiple logs on REJECT

This patch adds support to verifier tests to check for a succession of
verifier log messages on program load failure. This makes the errstr
field work uniformly across REJECT and VERBOSE_ACCEPT checks.

This patch also increases the maximum size of a message in the series of
messages to test from 80 chars to 200 chars. This is in order to keep
existing tests working, which sometimes test for messages larger than 80
chars (which was accepted in the REJECT case, when testing for a single
message, but not in the VERBOSE_ACCEPT case, when testing for possibly
multiple messages).

And example of such a long, checked message is in bounds.c: "R1 has
unknown scalar with mixed signed bounds, pointer arithmetic with it
prohibited for !root"
Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20210130220150.59305-1-andreimatei1@gmail.com

tools/testing/selftests/bpf/test_verifier.c

@@ -88,6 +88,10 @@ struct bpf_test {
 	int fixup_map_event_output[MAX_FIXUPS];
 	int fixup_map_reuseport_array[MAX_FIXUPS];
 	int fixup_map_ringbuf[MAX_FIXUPS];
+	/* Expected verifier log output for result REJECT or VERBOSE_ACCEPT.
+	 * Can be a tab-separated sequence of expected strings. An empty string
+	 * means no log verification.
+	 */
 	const char *errstr;
 	const char *errstr_unpriv;
 	uint32_t insn_processed;
@@ -995,13 +999,19 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
 	return 0;
 }
 
+/* Returns true if every part of exp (tab-separated) appears in log, in order.
+ *
+ * If exp is an empty string, returns true.
+ */
 static bool cmp_str_seq(const char *log, const char *exp)
 {
-	char needle[80];
+	char needle[200];
 	const char *p, *q;
 	int len;
 
 	do {
+		if (!strlen(exp))
+			break;
 		p = strchr(exp, '\t');
 		if (!p)
 			p = exp + strlen(exp);
@@ -1015,7 +1025,7 @@ static bool cmp_str_seq(const char *log, const char *exp)
 		needle[len] = 0;
 		q = strstr(log, needle);
 		if (!q) {
-			printf("FAIL\nUnexpected verifier log in successful load!\n"
+			printf("FAIL\nUnexpected verifier log!\n"
 			       "EXP: %s\nRES:\n", needle);
 			return false;
 		}
@@ -1130,7 +1140,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 			printf("FAIL\nUnexpected success to load!\n");
 			goto fail_log;
 		}
-		if (!expected_err || !strstr(bpf_vlog, expected_err)) {
+		if (!expected_err || !cmp_str_seq(bpf_vlog, expected_err)) {
 			printf("FAIL\nUnexpected error message!\n\tEXP: %s\n\tRES: %s\n",
 			      expected_err, bpf_vlog);
 			goto fail_log;