[Qemu-devel] PATCH: Close file descriptors when execing network tap setup script

["Daniel P. Berrange" <berrange@redhat.com>]

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In the VM initialization, the files corresponding to the virtual disks are
opened before the networking is setup. So when the time comes to run the
network tap setup script the QEMU process has a bunch of open file handles
which are leaked to the networking script. Some of the commands run by the
networking script may well be executing under a confined SELinux domain so
this leak of file handles triggers security audit alerts / denials.

The attached patch explicitly closes all file handles prior to execing the 
network script, except for STDIN/OUT/ERR and the TAP file handle itself.

Regards,
Dan.
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Index: vl.c
===================================================================
RCS file: /sources/qemu/qemu/vl.c,v
retrieving revision 1.260
diff -u -p -r1.260 vl.c
--- vl.c	28 Feb 2007 21:59:44 -0000	1.260
+++ vl.c	6 Mar 2007 16:23:26 -0000
@@ -3620,6 +3620,14 @@ static int net_tap_init(VLANState *vlan,
         pid = fork();
         if (pid >= 0) {
             if (pid == 0) {
+                int open_max = sysconf (_SC_OPEN_MAX), i;
+                for (i = 0; i < open_max; i++)
+                    if (i != STDIN_FILENO &&
+                        i != STDOUT_FILENO &&
+                        i != STDERR_FILENO &&
+                        i != fd)
+                        close(i);
+
                 parg = args;
                 *parg++ = (char *)setup_script;
                 *parg++ = ifname;