selftests: bpf: test_sockmap: handle file creation failures gracefully

test_sockmap creates a temporary file to use for sendpage.
this may fail for various reasons. Handle the error rather
than segfault.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/test_sockmap.c

@@ -332,6 +332,10 @@ static int msg_loop_sendpage(int fd, int iov_length, int cnt,
 	int i, fp;
 
 	file = fopen(".sendpage_tst.tmp", "w+");
+	if (!file) {
+		perror("create file for sendpage");
+		return 1;
+	}
 	for (i = 0; i < iov_length * cnt; i++, k++)
 		fwrite(&k, sizeof(char), 1, file);
 	fflush(file);
@@ -339,6 +343,11 @@ static int msg_loop_sendpage(int fd, int iov_length, int cnt,
 	fclose(file);
 
 	fp = open(".sendpage_tst.tmp", O_RDONLY);
+	if (fp < 0) {
+		perror("reopen file for sendpage");
+		return 1;
+	}
+
 	clock_gettime(CLOCK_MONOTONIC, &s->start);
 	for (i = 0; i < cnt; i++) {
 		int sent = sendfile(fd, fp, NULL, iov_length);