When initializing the child for a detached proxy, if the original pro…

…cess is the foreground process for its controlling terminal, try to make the new process the foreground process for the terminal.

Resolves #3875

CMakeLists.txt

@@ -1507,6 +1507,7 @@ set(TESTS_WITH_PROGRAM
   crash_in_function
   daemon_read
   dconf_mock
+  detach_terminal
   dev_tty
   x86/diversion_rdtsc
   diversion_sigtrap

src/RecordCommand.cc

@@ -817,6 +817,30 @@ static void reset_uid_sudo() {
   prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_CLEAR_ALL, 0, 0, 0);
 }
 
+static ScopedFd open_controlling_terminal_if_foreground_process_group_leader() {
+  char path[L_ctermid + 1];
+  ctermid(path);
+  ScopedFd terminal_fd(path, O_RDONLY);
+  if (terminal_fd.is_open()) {
+    pid_t fg_process_group = tcgetpgrp(terminal_fd);
+    if (fg_process_group != getpid()) {
+      terminal_fd.close();
+    }
+  }
+  return terminal_fd;
+}
+
+static void detach_teleport() {
+  int ret = syscall(SYS_rrcall_detach_teleport, (uintptr_t)0, (uintptr_t)0,
+    (uintptr_t)0, (uintptr_t)0, (uintptr_t)0, (uintptr_t)0);
+  if (ret < 0) {
+    FATAL() << "Failed to detach from parent rr";
+  }
+  if (running_under_rr(false)) {
+    FATAL() << "Detaching from parent rr did not work";
+  }
+}
+
 int RecordCommand::run(vector<string>& args) {
   RecordFlags flags;
   while (parse_record_arg(args, flags)) {
@@ -829,14 +853,28 @@ int RecordCommand::run(vector<string>& args) {
         return 1;
       case NESTED_DETACH:
       case NESTED_RELEASE: {
-        int ret = syscall(SYS_rrcall_detach_teleport, (uintptr_t)0, (uintptr_t)0,
-          (uintptr_t)0, (uintptr_t)0, (uintptr_t)0, (uintptr_t)0);
-        if (ret < 0) {
-          FATAL() << "Failed to detach from parent rr";
+        bool is_process_group_leader = getpgrp() == getpid();
+        ScopedFd terminal_fd = open_controlling_terminal_if_foreground_process_group_leader();
+
+        detach_teleport();
+
+        if (is_process_group_leader) {
+          setpgid(0, 0);
         }
-        if (running_under_rr(false)) {
-          FATAL() << "Detaching from parent rr did not work";
+        if (terminal_fd.is_open()) {
+          struct sigaction sa;
+          struct sigaction sa_old;
+          memset(&sa, 0, sizeof(sa));
+          sa.sa_handler = SIG_IGN;
+          // Ignore SIGTTOU while we change settings, we don't want it to stop us
+          sigaction(SIGTTOU, &sa, &sa_old);
+          int ret = tcsetpgrp(terminal_fd, getpid());
+          if (ret) {
+            LOG(warn) << "Failed to make ourselves the foreground process: " << errno_name(errno);
+          }
+          sigaction(SIGTTOU, &sa_old, nullptr);
         }
+
         if (flags.nested == NESTED_RELEASE) {
           exec_child(args);
           return 1;

src/test/detach_terminal.c

@@ -0,0 +1,76 @@
+/* -*- Mode: C; tab-width: 8; c-basic-offset: 2; indent-tabs-mode: nil; -*- */
+
+#include "util.h"
+
+int main(int argc, char** argv, char** envp) {
+  struct sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  sa.sa_handler = SIG_IGN;
+  sigaction(SIGTTIN, &sa, NULL);
+  sigaction(SIGTTOU, &sa, NULL);
+
+  if (argc >= 2 && strcmp(argv[1], "--newtty") == 0) {
+    int parent_to_child[2];
+    pipe(parent_to_child);
+    int child_to_parent[2];
+    pipe(child_to_parent);
+
+    // To call setsid() successfully this process must not be a
+    // process group leader. Create a child process, make it a process
+    // group leader, and move our process into that process group.
+    pid_t child = fork();
+    if (child == 0) {
+      test_assert(setpgid(0, 0) == 0);
+      test_assert(write(child_to_parent[1], "x", 1) == 1);
+      char ch;
+      test_assert(read(parent_to_child[0], &ch, 1) == 1);
+      return 0;
+    }
+    char ch;
+    test_assert(read(child_to_parent[0], &ch, 1) == 1);
+    test_assert(setpgid(getpid(), child) == 0);
+    test_assert(write(parent_to_child[1], "x", 1) == 1);
+
+    int status;
+    wait(&status);
+    test_assert(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+
+    test_assert(setsid() >= 0);
+
+    // Create a new terminal, make it the controlling terminal
+    // for this process, and exec the rest of the command line.
+    int control_fd = posix_openpt(O_RDWR);
+    test_assert(control_fd >= 0);
+    test_assert(grantpt(control_fd) == 0);
+    test_assert(unlockpt(control_fd) == 0);
+
+    char buf[PATH_MAX];
+    ptsname_r(control_fd, buf, sizeof(buf));
+    int term_fd = open(buf, O_RDWR);
+    test_assert(term_fd >= 0);
+
+    test_assert(dup2(term_fd, STDIN_FILENO) == STDIN_FILENO);
+
+    execve(argv[2], argv + 2, envp);
+    return 65;
+  }
+
+  if (argc >= 2 && strcmp(argv[1], "--newpgrp") == 0) {
+    // Make this process the foreground process for our terminal
+    // and exec the rest of the command line.
+    test_assert(setpgrp() >= 0);
+    test_assert(tcsetpgrp(STDIN_FILENO, getpid()) >= 0);
+    execve(argv[2], argv + 2, envp);
+    return 66;
+  }
+
+  // Check that we are the foreground process for our terminal.
+  int pgrp = tcgetpgrp(STDIN_FILENO);
+  if (pgrp != getpid()) {
+    atomic_printf("tcgetpgrp() == %d, expected %d\n", pgrp, getpid());
+    return 67;
+  }
+
+  atomic_puts("EXIT-SUCCESS");
+  return 0;
+}

src/test/detach_terminal.run

@@ -0,0 +1,7 @@
+source `dirname $0`/util.sh
+skip_if_test_32_bit
+actual_rr=$(which $RR_EXE)
+RR_EXE="detach_terminal$bitness --newtty $actual_rr"
+just_record detach_terminal$bitness "--newpgrp $actual_rr record --nested=release detach_terminal$bitness"
+replay
+check_record EXIT-SUCCESS