Re: dma(8): Fix race condition in multi-recipient delivery

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

Simon 'corecode' Schubert wrote:
> Uh.  I ment to add a dup() there, but I moved a lot of code, so I 
> forgot...  What about the attached patch?

And of course I attached the wrong one.  Here the right one.

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From 89024d4f2123e609e736fb745e5fb0b1973548fe Mon Sep 17 00:00:00 2001
From: Simon Schubert <simon.schubert@epfl.ch>
Date: Thu, 9 Jul 2009 23:24:35 +0200
Subject: [PATCH] dma: prevent races from sharing fd between children

On fork, fds are shared between children.  If two processes work on
different recipients, but on the same queue file, they might get
confused when the fd (and thus the offset) is shared.  Prevent this by
re-opening the fd after fork.

Reported-by: Daniel Roethlisberger <daniel@roe.ch>
---
 libexec/dma/dma.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/libexec/dma/dma.c b/libexec/dma/dma.c
index 4633b0c..08fc8fb 100644
--- a/libexec/dma/dma.c
+++ b/libexec/dma/dma.c
@@ -484,6 +484,7 @@ go_background(struct queue *queue)
 {
 	struct sigaction sa;
 	struct qitem *it;
+	FILE *newqf;
 	pid_t pid;
 
 	if (daemonize && daemon(0, 0) != 0) {
@@ -515,6 +516,17 @@ go_background(struct queue *queue)
 			 *
 			 * return and deliver mail
 			 */
+			/*
+			 * We have to prevent sharing of fds between children, so
+			 * we have to dup the queue fd.
+			 */
+			newqf = fdopen(dup(fileno(it->queuef)), "r");
+			if (newqf == NULL) {
+				syslog(LOG_ERR, "can not dup queue fd: %m");
+				exit(1);
+			}
+			fclose(it->queuef);
+			it->queuef = newqf;
 			return (it);
 
 		default:
-- 
1.6.2.149.g6462