Re: [PATCH net-next v4 3/3] vsock/test: Expand linger test to ensure close() does not misbehave

[Stefano Garzarella]

On Thu, May 01, 2025 at 10:05:24AM +0200, Michal Luczaj wrote:

There was an issue with SO_LINGER: instead of blocking until all queued
messages for the socket have been successfully sent (or the linger timeout
has been reached), close() would block until packets were handled by the
peer.

This is a new behaviour that only new kernels will follow, so I think
it is better to add a new test instead of extending a pre-existing test
that we described as "SOCK_STREAM SO_LINGER null-ptr-deref".

The old test should continue to check the null-ptr-deref also for old
kernels, while the new test will check the new behaviour, so we can skip
the new test while testing an old kernel.

Thanks,
Stefano

Add a check to alert on close() lingering when it should not.

Signed-off-by: Michal Luczaj <m...@rbox.co>
---
tools/testing/vsock/vsock_test.c | 30 +++++++++++++++++++++++++++---
1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index 
d0f6d253ac72d08a957cb81a3c38fcc72bec5a53..82d0bc20dfa75041f04eada1b4310be2f7c3a0c1
 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1788,13 +1788,16 @@ static void test_stream_connect_retry_server(const 
struct test_opts *opts)
        close(fd);
}

+#define        LINGER_TIMEOUT  1       /* seconds */
+
static void test_stream_linger_client(const struct test_opts *opts)
{
        struct linger optval = {
                .l_onoff = 1,
-               .l_linger = 1
+               .l_linger = LINGER_TIMEOUT
        };
-       int fd;
+       int bytes_unsent, fd;
+       time_t ts;

        fd = vsock_stream_connect(opts->peer_cid, opts->peer_port);
        if (fd < 0) {
@@ -1807,7 +1810,28 @@ static void test_stream_linger_client(const struct 
test_opts *opts)
                exit(EXIT_FAILURE);
        }

+       /* Byte left unread to expose any incorrect behaviour. */
+       send_byte(fd, 1, 0);
+
+       /* Reuse LINGER_TIMEOUT to wait for bytes_unsent == 0. */
+       timeout_begin(LINGER_TIMEOUT);
+       do {
+               if (ioctl(fd, SIOCOUTQ, &bytes_unsent) < 0) {
+                       perror("ioctl(SIOCOUTQ)");
+                       exit(EXIT_FAILURE);
+               }
+               timeout_check("ioctl(SIOCOUTQ) == 0");
+       } while (bytes_unsent != 0);
+       timeout_end();
+
+       ts = current_nsec();
        close(fd);
+       if ((current_nsec() - ts) / NSEC_PER_SEC > 0) {
+               fprintf(stderr, "Unexpected lingering on close()\n");
+               exit(EXIT_FAILURE);
+       }
+
+       control_writeln("DONE");
}

static void test_stream_linger_server(const struct test_opts *opts)
@@ -1820,7 +1844,7 @@ static void test_stream_linger_server(const struct 
test_opts *opts)
                exit(EXIT_FAILURE);
        }

-       vsock_wait_remote_close(fd);
+       control_expectln("DONE");
        close(fd);
}


--
2.49.0