2 files changed, 64 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index 3b9814f51..7b8212505 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -38,6 +38,12 @@
      [sshconnect1.c sshconnect2.c sshconnect.c sshd.8 sshd.c sshd_config]
      [ssh-keygen.c sshlogin.c sshpty.c sshtty.c ttymodes.c uidswap.c]
      basic KNF done while i was looking for something else
+   - markus@cvs.openbsd.org 2001/12/19 16:09:39
+     [serverloop.c]
+     fix race between SIGCHLD and select with an additional pipe.  writing
+     to the pipe on SIGCHLD wakes up select(). using pselect() is not
+     portable and siglongjmp() ugly. W. R. Stevens suggests similar solution.
+     initial idea by pmenage@ensim.com; ok deraadt@, djm@
 
 20011219
  - (stevesk) OpenBSD CVS sync X11 localhost display
@@ -7066,4 +7072,4 @@
  - Wrote replacements for strlcpy and mkdtemp
  - Released 1.0pre1
 
-$Id: ChangeLog,v 1.1701 2001/12/21 03:45:46 djm Exp $
+$Id: ChangeLog,v 1.1702 2001/12/21 03:53:11 djm Exp $
diff --git a/serverloop.c b/serverloop.c
index 1fa1f5800..c876dc0ca 100644
--- a/serverloop.c
+++ b/serverloop.c
@@ -35,7 +35,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: serverloop.c,v 1.86 2001/12/19 07:18:56 deraadt Exp $");
+RCSID("$OpenBSD: serverloop.c,v 1.87 2001/12/19 16:09:39 markus Exp $");
 
 #include "xmalloc.h"
 #include "packet.h"
@@ -92,6 +92,51 @@ static volatile sig_atomic_t child_terminated = 0;	/* The child has terminated.
 /* prototypes */
 static void server_init_dispatch(void);
 
+/*
+ * we write to this pipe if a SIGCHLD is caught in order to avoid
+ * the race between select() and child_terminated
+ */
+static int notify_pipe[2];
+static void
+notify_setup(void)
+{
+        if (pipe(notify_pipe) < 0) {
+                error("pipe(notify_pipe) failed %s", strerror(errno));
+        } else if ((fcntl(notify_pipe[0], F_SETFD, 1) == -1) ||
+            (fcntl(notify_pipe[1], F_SETFD, 1) == -1)) {
+                error("fcntl(notify_pipe, F_SETFD) failed %s", strerror(errno));
+                close(notify_pipe[0]);
+                close(notify_pipe[1]);
+        } else {
+                set_nonblock(notify_pipe[0]);
+                set_nonblock(notify_pipe[1]);
+                return;
+        }
+        notify_pipe[0] = -1;    /* read end */
+        notify_pipe[1] = -1;    /* write end */
+}
+static void
+notify_parent(void)
+{
+        if (notify_pipe[1] != -1)
+                write(notify_pipe[1], "", 1);
+}
+static void
+notify_prepare(fd_set *readset)
+{
+        if (notify_pipe[0] != -1)
+                FD_SET(notify_pipe[0], readset);
+}
+static void
+notify_done(fd_set *readset)
+{
+        char c;
+
+        if (notify_pipe[0] != -1 && FD_ISSET(notify_pipe[0], readset))
+                while (read(notify_pipe[0], &c, 1) != -1)
+                        debug2("notify_done: reading");
+}
+
 static void
 sigchld_handler(int sig)
 {
@@ -99,6 +144,7 @@ sigchld_handler(int sig)
         debug("Received SIGCHLD.");
         child_terminated = 1;
         mysignal(SIGCHLD, sigchld_handler);
+        notify_parent();
         errno = save_errno;
 }
 
@@ -242,6 +288,7 @@ wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp, int *maxfdp,
                 if (fdin != -1 && buffer_len(&stdin_buffer) > 0)
                         FD_SET(fdin, *writesetp);
         }
+        notify_prepare(*readsetp);
 
         /*
          * If we have buffered packet data going to the client, mark that
@@ -279,6 +326,8 @@ wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp, int *maxfdp,
                         error("select: %.100s", strerror(errno));
         } else if (ret == 0 && client_alive_scheduled)
                 client_alive_check();
+
+        notify_done(*readsetp);
 }
 
 /*
@@ -468,6 +517,8 @@ server_loop(pid_t pid, int fdin_arg, int fdout_arg, int fderr_arg)
         connection_in = packet_get_connection_in();
         connection_out = packet_get_connection_out();
 
+        notify_setup();
+
         previous_stdout_buffer_bytes = 0;
 
         /* Set approximate I/O buffer size. */
@@ -573,6 +624,7 @@ server_loop(pid_t pid, int fdin_arg, int fdout_arg, int fderr_arg)
                 max_fd = MAX(max_fd, fdin);
                 max_fd = MAX(max_fd, fdout);
                 max_fd = MAX(max_fd, fderr);
+                max_fd = MAX(max_fd, notify_pipe[0]);
 
                 /* Sleep in select() until we can do something. */
                 wait_until_can_do_something(&readset, &writeset, &max_fd,
@@ -697,7 +749,11 @@ server_loop2(Authctxt *authctxt)
         connection_in = packet_get_connection_in();
         connection_out = packet_get_connection_out();
 
+        notify_setup();
+
         max_fd = MAX(connection_in, connection_out);
+        max_fd = MAX(max_fd, notify_pipe[0]);
+
         xxx_authctxt = authctxt;
 
         server_init_dispatch();