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Re: [Qemu-block] [Qemu-devel] [PATCH 2/8] block: fix unbounded stack for

From: Paolo Bonzini
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 2/8] block: fix unbounded stack for dump_qdict
Date: Tue, 8 Mar 2016 13:17:03 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 08/03/2016 09:12, Markus Armbruster wrote:
> I'm afraid this isn't a good idea.  It relies on the non-local argument
> that nobody will ever put a key longer than 255 into a qdict that gets
> dumped.  That may even be the case, but you need to *prove* it, not just
> assert it.  The weakest acceptable proof might be assertions in every
> place that put keys into a dict that might get dumped.  I suspect that's
> practical and maintainable only if there's a single place that does it.
> If this was a good idea, I'd recommend to avoid the awkward macro:
>            char key[256];
>            int i;
>            assert(strlen(entry->key) + 1 <= ARRAY_SIZE(key));
> There are several other ways to limit the stack usage:
> 1. Move the array from stack to heap.  Fine unless it's on a hot path.
>    As far as I can tell, this dumping business is for HMP and qemu-io,
>    i.e. not hot.

I think this is the best.  You can just g_strdup, modify in place, print
and free.


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