Re: [PATCH] docs: show how to spawn qemu-storage-daemon with fd passing

[Daniel P . Berrangé]

On Mon, Mar 01, 2021 at 09:49:21AM -0600, Eric Blake wrote:
> On 3/1/21 9:41 AM, Daniel P. Berrangé wrote:
> > On Mon, Mar 01, 2021 at 03:31:59PM +0000, Stefan Hajnoczi wrote:
> >> The QMP monitor, NBD server, and vhost-user-blk export all support file
> >> descriptor passing. This is a useful technique because it allows the
> >> parent process to spawn and wait for qemu-storage-daemon without busy
> >> waiting, which may delay startup due to arbitrary sleep() calls.
> >>
> >> This Python example is inspired by the test case written for libnbd by
> >> Richard W.M. Jones <rjones@redhat.com>:
> >> https://gitlab.com/nbdkit/libnbd/-/commit/89113f484effb0e6c322314ba75c1cbe07a04543
> >>
> >> Thanks to Daniel P. Berrangé <berrange@redhat.com> for suggestions on
> >> how to get this working. Now let's document it!
> >>
> 
> >> +  sock_path = '/tmp/qmp-{}.sock'.format(os.getpid())
> > 
> > Example code inevitably gets cut+paste into real world apps, and this
> > example is a tmpfile CVE flaw. At least put it in $CWD instead.
> 
> Except $CWD may be too long for a sock file name to be created.
> Creating the sock in a securely-created subdirectory of /tmp is more
> reliable.

$XDG_RUNTIME_DIR then, which is /run/user/$UID, so safely per user on all
modern OS.


Regards,
Daniel
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