On Tue, Aug 19, 2008 at 10:51:29PM +0200, Jim Meyering wrote:
"Daniel P. Berrange" <berrange@redhat.com> wrote:
Some of the existing usage of fork/exec in libvirt is done such that the child process is daemonized. In particular the libvirt_proxy and the auto-spawned libvirtd for qemu:///session. Since we want to switch these to use virExec, we need to suport a daemon mode.
This patch removes the two alternate virExec and virExecNonBlock functions and renames the internal __virExec to virExec. It then gains a 'flags' parameter which can be used to specify non-blocking mode, or daemon mode.
We also add the ability to pass in a list of environment variables which get passed on to execve(). We also now explicitly close all file handles. Although libvirt code is careful to set O_CLOSEXEC on all its file handles, in multi-threaded apps there is a race condition between opening a FD and setting O_CLOSEXEC. Furthermore, we can't guarentee that all applications using libvirt are careful to set O_CLOSEXEC. Leaking FDs to a child is a potential security risk and often causes SELinux AVCs to be raised. Thus explicitely closing all FDs is a important safety net.
How about closing those FDs in the child instead, right after the fork? Then, if a virExec caller has an open socket or file descriptor, it won't be closed behind its back.
This is being done after a fork(). The diff context in this patch is a little misleading. The fork() shown here is the 2nd optional fork() done in daemon mode. The first fork() is higher up before we close the FDs.
diff -r 28ddf9f5791c src/util.c ... + for (i = 3; i < openmax; i++) + if (i != infd && + i != null && + i != childout && + i != childerr) + close(i); + + if (flags & VIR_EXEC_DAEMON) { + if (setsid() < 0) { + ReportError(conn, VIR_ERR_INTERNAL_ERROR, + _("cannot become session leader: %s"), + strerror(errno)); + _exit(1); + } + + if (chdir("/") < 0) { + ReportError(conn, VIR_ERR_INTERNAL_ERROR, + _("cannot change to root directory: %s"), + strerror(errno)); + _exit(1); + } + + pid = fork(); ...
Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|