On 251014 0030, Navid Emamdoost wrote:
> Add a new generic fuzz target for the QEMU VNC server. This target
> exercises both the standard VNC protocol and the VNC-over-WebSocket
> transport layer, increasing coverage of a primary remote attack surface.
>
> To support parallel fuzzing (e.g., with oss-fuzz), the VNC unix
> socket paths are generated dynamically. The fuzzer harness inspects the
> command line for placeholders and replaces them with unique paths
> created by mkstemp() before execution.
>
> ---
>
> This new target increases code coverage in the VNC subsystem
> and related networking and I/O code.
> The baseline coverage below was generated by running all existing fuzz
> targets with the oss-fuzz corpus. The new target shows significant gains:
>
> ----------------------------------------------------------------------------
> File New Target Baseline Change
> ----------------------------------------------------------------------------
> vnc.c 339/3212 (10.6%) 3/3212 (0.1%) +336
> keymaps.c 91/184 (49.5%) 0/184 (0.0%) +91
> net-listener.c 76/198 (38.4%) 3/198 (1.5%) +73
> channel-socket.c 73/575 (12.7%) 19/575 (3.3%) +54
> qemu-sockets.c 44/1019 (4.3%) 0/1019 (0.0%) +44
> vnc-jobs.c 41/219 (18.7%) 0/219 (0.0%) +41
> dns-resolver.c 28/145 (19.3%) 3/145 (2.1%) +25
>
> Signed-off-by: Navid Emamdoost <[email protected]>
> ---
> tests/qtest/fuzz/fuzz.c | 65 +++++++++++++++++++++++++
> tests/qtest/fuzz/generic_fuzz_configs.h | 5 ++
> 2 files changed, 70 insertions(+)
>
> diff --git a/tests/qtest/fuzz/fuzz.c b/tests/qtest/fuzz/fuzz.c
> index ca248a51a6..b77c3ceb2b 100644
> --- a/tests/qtest/fuzz/fuzz.c
> +++ b/tests/qtest/fuzz/fuzz.c
> @@ -126,6 +126,46 @@ static FuzzTarget *fuzz_get_target(char* name)
> return NULL;
> }
>
> +/*
> + * Global variables to hold the unique socket paths for cleanup.
> + */
> +static char g_vnc_socket_path[sizeof("/tmp/qemu-vnc.XXXXXX")];
> +static char g_vnc_ws_socket_path[sizeof("/tmp/qemu-vnc-ws.XXXXXX")];
> +
> +/*
> + * atexit() handler to clean up both socket files.
> + */
> +static void cleanup_vnc_sockets(void)
> +{
> + if (g_vnc_socket_path[0] != '\0') {
> + unlink(g_vnc_socket_path);
> + }
> + if (g_vnc_ws_socket_path[0] != '\0') {
> + unlink(g_vnc_ws_socket_path);
> + }
> +}
> +
> +/* Helper function to find and replace a placeholder in a GString */
> +static bool replace_socket_placeholder(GString *cmd_line, const char
> *placeholder,
> + const char *path_template, char
> *global_path_out)
> +{
> + char *placeholder_ptr = strstr(cmd_line->str, placeholder);
> + if (placeholder_ptr) {
> + int fd;
> + strcpy(global_path_out, path_template);
> + fd = mkstemp(global_path_out);
Appologies for the delay. Let's use g_mkstemp, if possible.
> + if (fd == -1) {
> + perror("mkstemp failed");
> + return false;
> + }
> + close(fd);
> +
> + gssize pos = placeholder_ptr - cmd_line->str;
> + g_string_erase(cmd_line, pos, strlen(placeholder));
> + g_string_insert(cmd_line, pos, global_path_out);
> + }
> + return true;
> +}
>
> /* Sometimes called by libfuzzer to mutate two inputs into one */
> size_t LLVMFuzzerCustomCrossOver(const uint8_t *data1, size_t size1,
> @@ -213,6 +253,31 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char
> ***envp)
> g_string_append_printf(cmd_line, " %s -qtest /dev/null ",
> getenv("QTEST_LOG") ? "" : "-qtest-log none");
>
> + /*
> + * For the VNC fuzzer, we replace placeholders for both the standard
> + * and WebSocket VNC listeners with unique socket paths.
> + */
> + if (strcmp(fuzz_target->name, "generic-fuzz-vnc") == 0) {
Can generic_fuzz_config.argfunc be used here, instead?
We use it for virtio_9p to create/share temp directories in
generic_fuzzer_virtio_9p_args. I would rather have one way of
dynamically generating arguments.
-Alex
> + bool success = true;
> + success &= replace_socket_placeholder(cmd_line, "VNC_SOCKET_PATH",
> + "/tmp/qemu-vnc.XXXXXX",
> g_vnc_socket_path);
> + success &= replace_socket_placeholder(cmd_line, "VNC_WS_SOCKET_PATH",
> + "/tmp/qemu-vnc-ws.XXXXXX",
> g_vnc_ws_socket_path);
> +
> + if (!success) {
> + exit(1);
> + }
> +
> + /* Check that placeholders were actually found and replaced */
> + if (g_vnc_socket_path[0] == '\0' || g_vnc_ws_socket_path[0] == '\0')
> {
> + fprintf(stderr, "ERROR: VNC fuzzer is missing a socket
> placeholder\n");
> + exit(1);
> + }
> +
> + /* Register a single cleanup handler for both sockets */
> + atexit(cleanup_vnc_sockets);
> + }
> +
> /* Split the runcmd into an argv and argc */
> wordexp_t result;
> wordexp(cmd_line->str, &result, 0);
> diff --git a/tests/qtest/fuzz/generic_fuzz_configs.h
> b/tests/qtest/fuzz/generic_fuzz_configs.h
> index ef0ad95712..bd2d875dd8 100644
> --- a/tests/qtest/fuzz/generic_fuzz_configs.h
> +++ b/tests/qtest/fuzz/generic_fuzz_configs.h
> @@ -247,6 +247,11 @@ const generic_fuzz_config predefined_configs[] = {
> .args = "-machine q35 -nodefaults "
> "-parallel file:/dev/null",
> .objects = "parallel*",
> + },{
> + .name = "vnc",
> + .args = "-machine q35 -nodefaults "
> + "-vnc
> vnc=unix:VNC_SOCKET_PATH,websocket=unix:VNC_WS_SOCKET_PATH",
> + .objects = "*",
> }
> };
>
> --
> 2.51.0.760.g7b8bcc2412-goog
>
