[dm-crypt] unsafe??? use of memset

Arno Wagner arno at wagner.name
Tue Dec 30 17:38:14 CET 2014


Interesting question. I think it is not relevant for most
Linux scenarios, as memset() comes precompiled as part of
a binary library, and the compiler has no clue what it 
does and hence cannot optimize it away. 

If memset is compiled together with the code using it, 
this would be a problem, but also one anybody writing
secure code should be aware of. I am not aware of any 
normal Linux scenarios where that could happen.

Still, soemthing low-priority to fix eventually, as 
it cannot be ruled out that it may some day be compiled
in a dangerous fashion or memset() may be made a macro
or some other bizarre circumstances.

BTW, with GCC, there is also the possibility to locally
prohibit optimization with something like:

#pragma GCC push_options
#pragma GCC optimize ("O0")
 code
#pragma GCC pop_options

I needed that some time ago, but do not remember for what.

Anyways, this is an area where recipes do not cut it. For
secure code you have to understand how it gets compiled 
on the specific target platform and what the issues there
are. 

Arno

On Tue, Dec 30, 2014 at 14:57:56 CET, .. ink .. wrote:
> a lot of people like this one[2] advises against the use of memset to clear
> memory but crypsetup seems to
> ignore this advice and use memset a lot like in[1].
> 
> Any reason why cryptseup is ignoring this advice?
> 
> [1]
> https://code.google.com/p/cryptsetup/source/browse/lib/tcrypt/tcrypt.c#272
> [2]
> http://edc.tversu.ru/elib/inf/0088/0596003943_secureprgckbk-chp-13-sect-2.html

> _______________________________________________
> dm-crypt mailing list
> dm-crypt at saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt


-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
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----
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