Re: Fuzz-test.sh crashes that can't be reproduced

[Peter Wu <peter () lekensteyn nl>]

Hey Nora,

On Wed, Dec 07, 2016 at 04:07:45PM -0800, Nora Sandler wrote:
> Hi list!
>
> I'm trying to do some fuzzing with fuzz-test.sh, and I'm seeing some strange behavior that I hope someone can help me 
> figure out. For every pcap I try, I get a crash pretty quickly, usually in less than 10 passes. But then I can't 
> reproduce the crash using test-captures.sh and the fuzzed output file. 
>
> I'm seeing this behavior using my own pcaps as well as captures from 
> https://wiki.wireshark.org/SampleCaptures#Sample_Captures. I'm running the latest code from the master branch on OS X 
> 10.12. It seems like it's heap corruption related since I stop getting crashes if I comment out the following lines 
> test-common.sh: 
>
> export MallocCheckHeapStart=1000
> export MallocCheckHeapEach=1000
>
> Here's some sample output:
>
> Fuzzing:
>
> $ ./tools/fuzz-test.sh -b ./build/run/ ~/Downloads/dhcp.pcap
> expr(15011,0x7fff9ab623c0) malloc: protecting edges
> expr(15011,0x7fff9ab623c0) malloc: enabling scribbling to detect mods to free blocks
> expr(15011,0x7fff9ab623c0) malloc: checks heap after 1000th operation and each 1000 operations
> expr(15011,0x7fff9ab623c0) malloc: will abort on heap corruption
> [...]
> mv(15166,0x7fff9ab623c0) malloc: will abort on heap corruption
> ./tools/fuzz-test.sh: line 203: 15155 Segmentation fault: 11  (core dumped) "$RUNNER" $COMMON_ARGS $ARGS 
> $TMP_DIR/$TMP_FILE > /dev/null 2>> $TMP_DIR/$ERR_FILE.$SUBSHELL_PID
> [...]
>
>  ERROR
> Processing failed. Capture info follows:
>
>   Input file: /Users/me/Downloads/dhcp.pcap
>   Output file: /tmp/fuzz-2016-12-07-15007.pcap
>   Pass: 6
> [...]
> stderr follows:
>
> cat(15181,0x7fff9ab623c0) malloc: protecting edges
> cat(15181,0x7fff9ab623c0) malloc: enabling scribbling to detect mods to free blocks
> cat(15181,0x7fff9ab623c0) malloc: checks heap after 1000th operation and each 1000 operations
> cat(15181,0x7fff9ab623c0) malloc: will abort on heap corruption
> Input file: /Users/me/Downloads/dhcp.pcap
>
> Build host information:
> Darwin my-machine.local 16.1.0 Darwin Kernel Version 16.1.0: Thu Oct 13 21:26:57 PDT 2016; 
> root:xnu-3789.21.3~60/RELEASE_X86_64 x86_64
> [...]
> Return value:  0
>
> Dissector bug:  0
>
> Valgrind error count:  0
> [...]
>
> And trying to reproduce the crash:
>
> $ ./tools/test-captures.sh -b ./build/run /tmp/fuzz-2016-12-07-15007.pcap
> Testing file /tmp/fuzz-2016-12-07-15007.pcap...
>  - with tree... sh(15256,0x7fff9ab623c0) malloc: protecting edges
> [...]
> OK
> [...]
>  - without tree... sh(15262,0x7fff9ab623c0) malloc: protecting edges
> [...]
> OK
>  - without tree but with a read filter... sh(15268,0x7fff9ab623c0) malloc: protecting edges
> [...]
> OK
>
> Is this an actual memory corruption bug in wireshark? A problem with the fuzzing script? Or am I doing something 
> wrong? I'd appreciate any suggestions you have.
>
> Thanks,
> Nora Sandler

Is it possible that the tool consumes a lot of memory, eventually
running out of memory and failing on allocations? Can you try to obtain
a coredump for post-mortem analysis?
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl
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