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

[Eric Blake]

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.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org