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 queue file after fork.

Reported-by: Daniel Roethlisberger <daniel@roe.ch>

diff --git a/dma.c b/dma.c
index 4633b0c6d3b9104cd76b7e48336affed7295507e..063c6b21c94aa4d43e33442574d462d48527c80d 100644 (file)
--- a/dma.c
+++ b/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 +516,18 @@ go_background(struct queue *queue)
                         *
                         * return and deliver mail
                         */
+                       /*
+                        * We have to prevent sharing of fds between children, so
+                        * we have to re-open the queue file.
+                        */
+                       newqf = fopen(it->queuefn, "r");
+                       if (newqf == NULL) {
+                               syslog(LOG_ERR, "can not re-open queue file `%s': %m",
+                                      it->queuefn);
+                               exit(1);
+                       }
+                       fclose(it->queuef);
+                       it->queuef = newqf;
                        return (it);
 
                default: