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); + 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) { + 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
