Fix race in pselect replacement code.

On the second and subsequent calls to pselect the notify_pipe was not
added to the select readset, opening up a race that om G. Christensen
discovered on multiprocessor Solaris <=9 systems.

Also reinitialize notify_pipe if the pid changes.  This will prevent a
parent and child from using the same FD, although this is not an issue
in the current structure it might be in future.

diff --git a/openbsd-compat/bsd-pselect.c b/openbsd-compat/bsd-pselect.c
index da34b41d8b69f93d2ff25886a6b1a7570867c002..983427aae5613c97db532568ec372fdac895635e 100644 (file)
--- a/openbsd-compat/bsd-pselect.c
+++ b/openbsd-compat/bsd-pselect.c
@@ -73,6 +73,7 @@ notify_setup_fd(int *fd)
  * we write to this pipe if a SIGCHLD is caught in order to avoid
  * the race between select() and child_terminated
  */
+static pid_t notify_pid;
 static int notify_pipe[2];
 static void
 notify_setup(void)
@@ -81,6 +82,15 @@ notify_setup(void)
 
        if (initialized)
                return;
+       if (notify_pid == 0)
+               debug3_f("initializing");
+       else {
+               debug3_f("pid changed, reinitializing");
+               if (notify_pipe[0] != -1)
+                       close(notify_pipe[0]);
+               if (notify_pipe[1] != -1)
+                       close(notify_pipe[1]);
+       }
        if (pipe(notify_pipe) == -1) {
                error("pipe(notify_pipe) failed %s", strerror(errno));
        } else if (notify_setup_fd(&notify_pipe[0]) == -1 ||
@@ -91,6 +101,9 @@ notify_setup(void)
        } else {
                set_nonblock(notify_pipe[0]);
                set_nonblock(notify_pipe[1]);
+               notify_pid = getpid();
+               debug3_f("pid %d saved %d pipe0 %d pipe1 %d", getpid(),
+                   notify_pid, notify_pipe[0], notify_pipe[1]);
                initialized = 1;
                return;
        }
@@ -159,15 +172,16 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
                if (sig == SIGKILL || sig == SIGSTOP || sigismember(mask, sig))
                        continue;
                if (sigaction(sig, NULL, &sa) == 0 &&
-                   sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL &&
-                   sa.sa_handler != sig_handler) {
+                   sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL) {
+                       unmasked = 1;
+                       if (sa.sa_handler == sig_handler)
+                               continue;
                        sa.sa_handler = sig_handler;
                        if (sigaction(sig, &sa, &osa) == 0) {
                                debug3_f("installing signal handler for %s, "
                                    "previous %p", strsignal(sig),
                                     osa.sa_handler);
                                saved_sighandler[sig] = osa.sa_handler;
-                               unmasked = 1;
                        }
                }
        }
@@ -183,7 +197,8 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
        saved_errno = errno;
        sigprocmask(SIG_SETMASK, &osig, NULL);
 
-       notify_done(readfds);
+       if (unmasked)
+               notify_done(readfds);
        errno = saved_errno;
        return ret;
 }