From: Ian Jackson <iwj@xenproject.org>
To: "Jürgen Groß" <jgross@suse.com>, "Julien Grall" <julien@xen.org>,
xen-devel@lists.xenproject.org, raphning@amazon.co.uk,
"Julien Grall" <jgrall@amazon.com>
Subject: Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters
Date: Fri, 5 Mar 2021 14:49:30 +0000 [thread overview]
Message-ID: <24642.17658.843482.352849@mariner.uk.xensource.com> (raw)
In-Reply-To: <24642.17467.425438.233285@mariner.uk.xensource.com>
Ian Jackson writes ("Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters"):
> Jürgen Groß writes ("Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters"):
> > On 05.03.21 15:37, Ian Jackson wrote:
> > > Jürgen Groß writes ("Re: [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters"):
> > >> This is the max number of 0 delimited string parameters. Especially the
> > >> stubdom case needs a binary blob (with length, of course) as parameter,
> > >> and the number of 0 bytes in this data is just limited by the allowed
> > >> payload length.
> > >>
> > >> See the comment in line 111 of xenstored_control.c.
> > >
> > > AFAICT this "live-update" command is variadic. So why is this
> > > parameter set here it all then ?
> >
> > In order to avoid allocating an array for 4000 arguments when there
> > are only 5 which need to be treated as strings.
>
> So this parameter is doing two jobs: 1. enabling non-variadic commands
> to take binary input; 2. preventing variadic commands from allocating
> unbounded memory.
>
> The problem with this is that in case 1 exceeding the value is normal
> and the final argument is binary data; whereas in case 2 glomming
> together the arguments together with zeroes is wrong and potentially
> hazrdous.
>
> I suggest we solve problem 2 by imposing a higher fixed (for all
> commands, variadic or not) limit (20 or something) which causes errors
> when exceeded, rather than silent argument misinterpretation.
Also, this use of max_pars to do job 2 seems very inconsistent. It is
applied only to "live-update".
If it is necessary for "live-update", which is it not necessary for
"check" or whatever ?
Ian.
next prev parent reply other threads:[~2021-03-05 14:49 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-05 12:10 [PATCH for-4.15] tools/xenstored: liveupdate: Increase the maximum number of parameters Julien Grall
2021-03-05 12:44 ` Jürgen Groß
2021-03-05 13:22 ` Ian Jackson
2021-03-05 14:33 ` Jürgen Groß
2021-03-05 14:37 ` Ian Jackson
2021-03-05 14:41 ` Jürgen Groß
2021-03-05 14:46 ` Ian Jackson
2021-03-05 14:49 ` Ian Jackson [this message]
2021-03-05 14:55 ` Jürgen Groß
2021-03-05 14:56 ` Jürgen Groß
2021-03-06 19:39 ` Julien Grall
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