Re: Kernel crypto framework, sleeping-in-atomic issues

[Vlad Yasevich <vyasevich@gmail.com>]

On 12/10/2015 10:49 AM, Fabrizio Demaria wrote:
> Hello,
> 
> I am investigating the current usage of kernel crypto-libraries in the
> SCTP code, considering to adopt the same crypto framework for the
> MPTCP implementation.
> 
> In sm_make_chunk.c, the crypto function "crypto_hash_setkey" is called
> in an atomic context, despite the fact that this function CAN invoke a
> GFP_KERNEL (sleeping) memory allocation. Calling a sleeping function
> from an atomic context can end up in deadlock. Has this factor been
> considered when adding the crypto functions into the SCTP code or has
> it been safely handled/verified in any way?

That code has been in use since the very beginning and we've never seen
any atomicity issues.  I think the reason for this is that we are only
using the sha1 hash code which doesn't seem to provide its own setkey
function.  What I think it's using is the hmac version of setkey (I could
be wrong here...) and that doesn't actually allocate any memory.

-vlad

> 
> 
> Thanks,
> Fabrizio
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