[systemd-devel] systemd should not depend on CONFIG_CRYPTO_USER_API_HASH

D.S. Ljungmark spider at aanstoot.se
Mon Mar 20 13:26:29 UTC 2017

I find your argument to be strange.

"The kernel has this functionality, please do not use it and rather
reimplement it in every piece of userspace that ever needs it, because
that's supposed to be more secure."

I simply don't buy your argument here.


On Mon, Mar 20, 2017 at 8:22 AM, Eric Biggers <ebiggers3 at gmail.com> wrote:
> Hello,
> The latest systemd README and NEWS claim that the userspace interface to the
> in-kernel hash algorithms (CONFIG_CRYPTO_USER_API_HASH) is now required.
> I don't know how much thought was put into this decision, but I think it's a
> mistake security-wise.  AF_ALG sockets increase the kernel's attack surface by
> allowing users to instantiate and use arbitrary crypto algorithms, in
> combinations or ways which may not have been tested.  Indeed, historically there
> have been a number of security vulnerabilities related to this feature, both in
> the API itself and in the various crypto modules.  For this reason, I think
> security-conscious users would prefer to have this kernel feature turned off.
> Why exactly does systemd suddenly need this feature?  If it's really just to
> compute hashes, then please do it in userspace instead.  Unless systemd *really*
> needs to support using hardware crypto accelerators, there is no need to call
> into the kernel just to compute hashes.  Or at the very least, make the
> dependency optional.
> Thanks!
> - Eric
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