Re: [libvirt] PATCH: 4/5: Support daemonizing child & env variables

On Tue, Aug 19, 2008 at 10:51:29PM +0200, Jim Meyering wrote: > "Daniel P. Berrange" <berrange(a)redhat.com&gt; 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.