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Re: [Qemu-devel] [PATCH] slirp: Fix packet expiration

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH] slirp: Fix packet expiration
Date: Tue, 27 Sep 2011 12:59:20 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2011-09-27 12:56, Fabien Chouteau wrote:
> On 27/09/2011 11:20, Thomas Huth wrote:
>> The two new variables "arp_requested" and "expiration_date" in the mbuf
>> structure have been added after the variable-sized "m_dat_" array. The
>> variables have to be added before the m_dat_ array instead.
>> Without this patch, the expiration_date gets clobbered by code that
>> accesses the m_dat_ array.
>> I experienced this problem with the code in slirp/tftp.c: The
>> tftp_send_data() function created a new packet with the m_get()
>> function (which fills-in a default expiration_date value). Then the
>> TFTP code cleared the data section of the packet, which accidentially
>> also cleared the expiration_date. This zeroed expiration_date then
>> finally causes the packet to be discarded during if_start(), so that
>> TFTP packets were not transmitted anymore.
> Thanks for the patch Thomas.
> I think we can add a comment to avoid this kind of mistake in the
> future.
> /* This is a "flexible array member". It should always remain
>  * the last member of the structure.
>  */

Good point, folded something like that in.


Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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