netdev - Re: Bug: tc filter show .... raise segfault if more than one rule with action -j MARK exist

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Message-ID: <536DEF16.6010406@a-greve.de>
Date:	Sat, 10 May 2014 11:19:18 +0200
From:	Andreas Greve <andreas.greve@...reve.de>
To:	stephen@...workplumber.org
CC:	netdev@...r.kernel.org, andreas.greve@...reve.de
Subject: Re: Bug: tc filter show .... raise segfault if more than one rule
 with action -j MARK exist

sorry its to early for me ;)

here the missing attachment.

On 05/10/14 11:11, Andreas Greve wrote:
> Dear Stephen Hemminger, Dear List Members,
>
> this is a corrected/optimized version of the patch
> Thanks to Stephen Hemminger, for giving me the hint to use structure 
> assignment instead of
> memcpy().
>
> Best wishes
>
> Andreas Greve
>
> On 05/08/14 13:48, Andreas Greve wrote:
>> Dear Stephen Hemminger, Dear List Members,
>>
>> the command
>>
>> tc filter show dev eth1 parent ffff:
>>
>> raise a segmentation fault if there are more than one filter rule 
>> with action -j MARK exists.
>>
>> Reason:
>> In print_ipt(...) xtables will be initialzed with a pointer to the 
>> static struct tcipt_globals at xtables_init_all(). Later on the 
>> fields .opts and .options_offset of tcipt_globals are modified. The 
>> call of xtables_free_opts(1) at the end of print_ipt(...) does not 
>> restore the original values of tcipt_globals for the modified fields. 
>> It only frees some allocated memory and sets .opts to NULL. This 
>> leads to a segmentation fault when print_ipt()
>> is called for the next filter rule with action -j MARK.
>>
>> Fix: (patch attached)
>> Cloneing tcipt_globals on the stack as tmp_tcipt_globals and use it 
>> instead of tcipt_globals, so tcipt_globals will be not modified.
>>
>> Tests:
>> I only have done limit tests for this fix ( action -j MARK ) on a 
>> debian wheezy iproute2 package build from source based on 
>> upstream/3.14.0. The system is a little bit special  kernel 
>> 3.12.17-xen on xen-4.4.1-pre.
>>
>>
>> Andreas Henriksson (debian iproute maintainer) give me an other idea 
>> of how to fix this bug by modifying  xtables_free_opts() so that it 
>> sets .opts = .orig_opts instead .opts = NULL. This should avoid 
>> having to duplicate the entire struct each time.
>>
>> I prefer the cloning  because:
>>
>> 1)  In my understanding the variable tcipt_globals is a complex 
>> "constant" that should never be modified. ( Is that right ?)
>>
>> 2) If we want to do the fix in xtables_free_opts we have to change 
>> the struct xtables_globals because we need for all fields .orig 
>> fields I think this will  make all things much more complicated.
>>
>>
>> additional Brainstorms:
>>
>> a ) Perhaps we have to think about of a deep clone of tcipt_globals 
>> to protect the underlaying option array
>> b ) makes cloning of  tcipt_globals sense in  parse_ipt(...)
>> But for this two decisions my understanding of the whole system is 
>> not enough.
>>
>>
>> I hope the Information helps
>>
>> Thanks
>>
>> Best wishes
>>
>>
>> Andreas Greve
>>
>>
>>
>>
>>
>>
>>
>>
>> Andreas Henriksson
>>
>>
>> Stephen Hemminger
>>
>


View attachment "0001-print_ipt-segfault-if-more-then-one-filter-with-acti.patch" of type "text/x-patch" (2794 bytes)