selftests/bpf: Only run tests if !bpf_disabled

The "kernel.unprivileged_bpf_disabled" sysctl, if enabled, causes all
unprivileged tests to fail because it permanently disables unprivileged
BPF access for the currently running kernel. Skip the relevant tests if
the user attempts to run the testsuite with this sysctl enabled.
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/test_verifier.c

@@ -57,6 +57,9 @@
 #define F_NEEDS_EFFICIENT_UNALIGNED_ACCESS	(1 << 0)
 #define F_LOAD_WITH_STRICT_ALIGNMENT		(1 << 1)
 
+#define UNPRIV_SYSCTL "kernel/unprivileged_bpf_disabled"
+static bool unpriv_disabled = false;
+
 struct bpf_test {
 	const char *descr;
 	struct bpf_insn	insns[MAX_INSNS];
@@ -11376,6 +11379,17 @@ static int set_admin(bool admin)
 	return ret;
 }
 
+static void get_unpriv_disabled()
+{
+	char buf[2];
+	FILE *fd;
+
+	fd = fopen("/proc/sys/"UNPRIV_SYSCTL, "r");
+	if (fgets(buf, 2, fd) == buf && atoi(buf))
+		unpriv_disabled = true;
+	fclose(fd);
+}
+
 static int do_test(bool unpriv, unsigned int from, unsigned int to)
 {
 	int i, passes = 0, errors = 0, skips = 0;
@@ -11386,7 +11400,10 @@ static int do_test(bool unpriv, unsigned int from, unsigned int to)
 		/* Program types that are not supported by non-root we
 		 * skip right away.
 		 */
-		if (!test->prog_type) {
+		if (!test->prog_type && unpriv_disabled) {
+			printf("#%d/u %s SKIP\n", i, test->descr);
+			skips++;
+		} else if (!test->prog_type) {
 			if (!unpriv)
 				set_admin(false);
 			printf("#%d/u %s ", i, test->descr);
@@ -11433,6 +11450,13 @@ int main(int argc, char **argv)
 		}
 	}
 
+	get_unpriv_disabled();
+	if (unpriv && unpriv_disabled) {
+		printf("Cannot run as unprivileged user with sysctl %s.\n",
+		       UNPRIV_SYSCTL);
+		return EXIT_FAILURE;
+	}
+
 	setrlimit(RLIMIT_MEMLOCK, unpriv ? &rlim : &rinf);
 	return do_test(unpriv, from, to);
 }