Re: [Qemu-devel] [Slirp] [PATCH 1/2] Do not reassemble fragments pointing outside of the original payload

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 8/29/19 5:43 PM, Philippe Mathieu-Daudé wrote:
> On 8/26/19 12:54 AM, Samuel Thibault wrote:
>> Philippe Mathieu-Daudé, le ven. 23 août 2019 17:15:32 +0200, a ecrit:
>>>> Did you make your test with commit 126c04acbabd ("Fix heap overflow in
>>>> ip_reass on big packet input") applied?
>>>
>>> Yes, unfortunately it doesn't fix the issue.
>>
>> Ok.
>>
>> Could you try the attached patch?  There was a use-after-free.  Without
>> it, I can indeed crash qemu with the given exploit.  With it I don't
>> seem to be able to crash it (trying in a loop for several minutes).
[...]
> 
> Note 2: We miss some Makefile rules in QEMU with the libslirp split.
> 
> Checkouting branches in the slirp/ directory doesn't trigger recompiling
> the slirp object, and even if I force the creation of the libslirp.a
> archive, the QEMU binaries are not linked again with the refreshed archive.

And I hit the same issue after applying your patch =)

So, using a clean workspace, I can not reproduce the null deref anymore.

If you send a proper patch, feel free to add:

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>

Thanks!

Phil.