selftests: tls: test TCP stealing data from under the TLS socket

Check a race where data disappears from the TCP socket after
TLS signaled that its ready to receive.

  ok 6 global.data_steal
  #  RUN           tls_basic.base_base ...
  #            OK  tls_basic.base_base

Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250807232907.600366-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

tools/testing/selftests/net/tls.c

@@ -2708,6 +2708,69 @@ TEST(prequeue) {
 	close(cfd);
 }
 
+TEST(data_steal) {
+	struct tls_crypto_info_keys tls;
+	char buf[20000], buf2[20000];
+	struct sockaddr_in addr;
+	int sfd, cfd, ret, fd;
+	int pid, status;
+	socklen_t len;
+
+	len = sizeof(addr);
+	memrnd(buf, sizeof(buf));
+
+	tls_crypto_info_init(TLS_1_2_VERSION, TLS_CIPHER_AES_GCM_256, &tls, 0);
+
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = htonl(INADDR_ANY);
+	addr.sin_port = 0;
+
+	fd = socket(AF_INET, SOCK_STREAM, 0);
+	sfd = socket(AF_INET, SOCK_STREAM, 0);
+
+	ASSERT_EQ(bind(sfd, &addr, sizeof(addr)), 0);
+	ASSERT_EQ(listen(sfd, 10), 0);
+	ASSERT_EQ(getsockname(sfd, &addr, &len), 0);
+	ASSERT_EQ(connect(fd, &addr, sizeof(addr)), 0);
+	ASSERT_GE(cfd = accept(sfd, &addr, &len), 0);
+	close(sfd);
+
+	ret = setsockopt(fd, IPPROTO_TCP, TCP_ULP, "tls", sizeof("tls"));
+	if (ret) {
+		ASSERT_EQ(errno, ENOENT);
+		SKIP(return, "no TLS support");
+	}
+	ASSERT_EQ(setsockopt(cfd, IPPROTO_TCP, TCP_ULP, "tls", sizeof("tls")), 0);
+
+	/* Spawn a child and get it into the read wait path of the underlying
+	 * TCP socket.
+	 */
+	pid = fork();
+	ASSERT_GE(pid, 0);
+	if (!pid) {
+		EXPECT_EQ(recv(cfd, buf, sizeof(buf), MSG_WAITALL),
+			  sizeof(buf));
+		exit(!__test_passed(_metadata));
+	}
+
+	usleep(2000);
+	ASSERT_EQ(setsockopt(fd, SOL_TLS, TLS_TX, &tls, tls.len), 0);
+	ASSERT_EQ(setsockopt(cfd, SOL_TLS, TLS_RX, &tls, tls.len), 0);
+
+	EXPECT_EQ(send(fd, buf, sizeof(buf), 0), sizeof(buf));
+	usleep(2000);
+	EXPECT_EQ(recv(cfd, buf2, sizeof(buf2), MSG_DONTWAIT), -1);
+	/* Don't check errno, the error will be different depending
+	 * on what random bytes TLS interpreted as the record length.
+	 */
+
+	close(fd);
+	close(cfd);
+
+	EXPECT_EQ(wait(&status), pid);
+	EXPECT_EQ(status, 0);
+}
+
 static void __attribute__((constructor)) fips_check(void) {
 	int res;
 	FILE *f;