fix: propagate SSH child setup failures

src/shared/transport_ssh.c

@@ -16,6 +16,12 @@ typedef struct {
   char* remote_path;
 } RemoteDest;
 
+static void ssh_child_setup_failed(int status_fd) {
+  ssize_t wret = write(status_fd, "x", 1);
+  (void)wret;
+  _exit(1);
+}
+
 static void remote_dest_destroy(RemoteDest* r) {
   free(r->user);
   free(r->host);
@@ -157,11 +163,12 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   if (pid == 0) {
     close(sv[0]);
     close(exec_pipe[0]);
-    fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC);
-    if (sv[1] != STDIN_FILENO)
-      dup2(sv[1], STDIN_FILENO);
-    if (sv[1] != STDOUT_FILENO)
-      dup2(sv[1], STDOUT_FILENO);
+    if (fcntl(exec_pipe[1], F_SETFD, FD_CLOEXEC) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDIN_FILENO && dup2(sv[1], STDIN_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
+    if (sv[1] != STDOUT_FILENO && dup2(sv[1], STDOUT_FILENO) < 0)
+      ssh_child_setup_failed(exec_pipe[1]);
     if (sv[1] > 1)
       close(sv[1]);
 
@@ -172,7 +179,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
       ssh_user_len = strlen(r.host) + 1;
     char* ssh_user = malloc(ssh_user_len);
     if (!ssh_user)
-      _exit(1);
+      ssh_child_setup_failed(exec_pipe[1]);
     if (r.user && r.user[0] != '\0')
       snprintf(ssh_user, ssh_user_len, "%s@%s", r.user, r.host);
     else
@@ -183,7 +190,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
     char port_str[16];
     char* remote_command = ssh_build_remote_command(server_path, old_args);
     if (!remote_command)
-      _exit(1);
+      ssh_child_setup_failed(exec_pipe[1]);
     ssh_argv[ac++] = "ssh";
     ssh_argv[ac++] = "-o";
     ssh_argv[ac++] = "Compression=no";
@@ -201,9 +208,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
     ssh_argv[ac] = NULL;
     execvp("ssh", ssh_argv);
     log_perror("exec of ssh failed");
-    ssize_t wret = write(exec_pipe[1], "x", 1);
-    (void)wret;
-    _exit(1);
+    ssh_child_setup_failed(exec_pipe[1]);
   }
 
   close(sv[1]);
@@ -213,7 +218,7 @@ Client* client_connect_ssh(const char* destination, int port, const char* server
   ssize_t n = read(exec_pipe[0], &exec_status, 1);
   close(exec_pipe[0]);
 
-  if (n > 0) {
+  if (n != 0) {
     close(sv[0]);
     waitpid(pid, NULL, 0);
     remote_dest_destroy(&r);

tests/test_transport_ssh.c

@@ -14,18 +14,23 @@ static void test_ssh_connect_invalid_dest_empty() {
   EXPECT_NULL(client);
 }
 
-/* Test client_connect_ssh with malformed destination (just a colon).
- * parse_remote_dest succeeds, ssh is exec'd and fails, but the function
- * creates a Client that must be cleaned up. */
+/* A child that cannot exec ssh must not be returned as a successful client. */
 static void test_ssh_connect_malformed() {
+  const char* old_path = getenv("PATH");
+  char* saved_path = old_path ? strdup(old_path) : NULL;
+  setenv("PATH", "", 1);
+
+  /* cppcheck-suppress constVariablePointer */
   Client* client = client_connect_ssh(":", 22, NULL, false);
-  /* ssh binary exists, so exec succeeds; the function returns a Client.
-   * We just verify it doesn't crash and clean up properly. */
-  if (client != NULL) {
-    client_disconnect(client);
-    client_delete(client);
+
+  if (saved_path) {
+    setenv("PATH", saved_path, 1);
+    free(saved_path);
+  } else {
+    unsetenv("PATH");
   }
-  EXPECT_TRUE(true);
+
+  EXPECT_NULL(client);
 }
 
 /* Test client_connect_ssh with valid format but unreachable host.