[openssl-dev] Question about valgrind error in DH in 1.0.2

[Kurt Cancemi]

Could this be the issue your seeing? It was fixed in boringssl I think.
https://boringssl.googlesource.com/boringssl/+/bf681a40d6142edfa44a27dc0d6e07e0c37865a4
https://boringssl-review.googlesource.com/#/c/1393/
---
Kurt Cancemi
https://www.x64architecture.com


On Wed, May 13, 2015 at 1:19 PM, John Foley <foleyj at cisco.com> wrote:
> Changing the movzwl to movzbl in bn_get_bits5 eliminates the valgrind
> error.  But this isn't a valid fix since bn_get_bits5 no longer returns
> the correct data.  My assembly skills are near nil.  Maybe someone else
> can propose a valid fix.
>
> Having said this, this does show the problem appears to be due to the
> movzwl reading past the end of the buffer by a byte.  Given the data
> allocated on the heap is likely surrounded by guard bytes, this is
> likely a benign read outside the buffer.  But it should still be fixed.
>
>
>
> On 05/13/2015 10:46 AM, John Foley wrote:
>> Sorry for misinterpreting your question, my mistake.  I was able to
>> replicate the error. It looks like the invalid read is in code that's
>> compiled in when OPENSSL_BN_ASM_MONT5 is set, which is only for the
>> X86_64 target.  Looking at the diff of x86_64-mont5.pl between 1.0.1 and
>> 1.0.2, there are quite a few changes.  My guess is this was introduced
>> in ec9cc70f72454b8d4a84247c86159613cee83b81.
>>
>>
>>
>>
>> On 05/13/2015 10:13 AM, Henrik Grindal Bakken wrote:
>>> John Foley <foleyj at cisco.com> writes:
>>>
>>>> If you add the --show-reachable option to valgrind, you can see where
>>>> the leaks originate.  They appear to be in the ex_data code (see
>>>> below).  As a side note, I see 416 bytes lost when using OpenSSL 1.0.1f
>>>> as well as 1.0.2a.
>>> Ah, I forgot to mention.  I'm not concerned about the leak, but the
>>> invalid read that's in 1.0.2 only.
>>>
>>> This one:
>>>
>>>>> ==14854== Invalid read of size 2
>>>>> ==14854== at 0x4F09198: bn_get_bits5 (in
>>>>> /home/henribak/src/thirdparty/openssl/libcrypto.so.1.0.0)
>>>>> ==14854== by 0x4F32B47: generate_key (in
>>>>> /home/henribak/src/thirdparty/openssl/libcrypto.so.1.0.0)
>>>>> ==14854==    by 0x400A30: main (in /home/henribak/tmp/dh-1.0.2)
>>
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