bug#9098: timeout should use waitpid

[Andreas Schwab]

timeout assumes that it only has to wait for a single child.  But this
is not true, it can always inherit other children from its predecessor:

$ sh -c "sleep 1 & exec timeout 2 sh -c 'sleep 3; echo foo'"

This will echo foo after three seconds, although the inner shell is
supposed to be killed after two seconds.

Andreas.

>From 331a32b8bbe3cc07d5522004e90fba2bde20a1c3 Mon Sep 17 00:00:00 2001
From: Andreas Schwab <address@hidden>
Date: Sat, 16 Jul 2011 13:51:06 +0200
Subject: [PATCH] timeout: ignore inherited children

* src/timeout.c (main): Use waitpid instead of wait.
---
 src/timeout.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/timeout.c b/src/timeout.c
index ef660a7..a5d42f4 100644
--- a/src/timeout.c
+++ b/src/timeout.c
@@ -358,14 +358,15 @@ main (int argc, char **argv)
 
       alarm (timeout);
 
-      /* We're just waiting for a single process here, so wait() suffices.
-         Note the signal() calls above on GNU/Linux and BSD at least,
+      /* Note the signal() calls above on GNU/Linux and BSD at least,
          essentially call the lower level sigaction() with the SA_RESTART flag
          set, which ensures the following wait call will only return if the
          child exits, not on this process receiving a signal. Also we're not
          passing WUNTRACED | WCONTINUED to a waitpid() call and so will not get
-         indication that the child has stopped or continued.  */
-      if (wait (&status) == -1)
+         indication that the child has stopped or continued.  We may have
+         inherited children from our predecessor, so a simple wait
+         doesn't suffice.  */
+      if (waitpid (monitored_pid, &status, 0) == -1)
         {
           /* shouldn't happen.  */
           error (0, errno, _("error waiting for command"));
-- 
1.7.6


-- 
Andreas Schwab, address@hidden
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