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List:       linux-keyrings
Subject:    Re: [PATCH] KEYS: Add ECDH support
From:       "Jarkko Sakkinen" <jarkko () kernel ! org>
Date:       2024-03-31 15:44:19
Message-ID: D081UQF5758Q.3TO9YN0PEQ0O1 () kernel ! org
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On Sat Mar 30, 2024 at 3:09 PM EET, James Bottomley wrote:
> On Sat, 2024-03-30 at 00:04 -0700, Eric Biggers wrote:
> > [+Cc linux-crypto]
> > 
> > On Sat, Mar 30, 2024 at 02:55:06PM +0800, Zhang Yiqun wrote:
> > > This patch is to introduce ECDH into keyctl syscall for
> > > userspace usage, containing public key generation and
> > > shared secret computation.
> > > 
> > > It is mainly based on dh code, so it has the same condition
> > > to the input which only user keys is supported. The output
> > > result is storing into the buffer with the provided length.
> > > 
> > > Signed-off-by: Zhang Yiqun <zhangyiqun@phytium.com.cn>
> > > ---
> > > Documentation/security/keys/core.rst |   62 ++++++
> > > include/linux/compat.h                             |     4 +
> > > include/uapi/linux/keyctl.h                   |   11 +
> > > security/keys/Kconfig                               |   12 +
> > > security/keys/Makefile                             |     2 +
> > > security/keys/compat_ecdh.c                   |   50 +++++
> > > security/keys/ecdh.c                                 | 318
> > > +++++++++++++++++++++++++++
> > > security/keys/internal.h                         |   44 ++++
> > > security/keys/keyctl.c                             |   10 +
> > > 9 files changed, 513 insertions(+)
> > > create mode 100644 security/keys/compat_ecdh.c
> > > create mode 100644 security/keys/ecdh.c
> > 
> > Nacked-by: Eric Biggers <ebiggers@google.com>
> > 
> > The existing KEYCTL_PKEY_*, KEYCTL_DH_COMPUTE, and AF_ALG are causing
> > enough problems.   We do not need any more UAPIs like this.   They are
> > hard to maintain, break often, not properly documented, increase the
> > kernel's attack surface, and what they do is better done in
> > userspace.
> 
> Actually that's not entirely true.  There is a use case for keys which
> is where you'd like to harden unwrapped key handling and don't have the
> ability to use a device.  The kernel provides a harder exfiltration
> environment than user space, so there is a use case for getting the
> kernel to handle operations on unwrapped keys for the protection it
> affords the crytpographic key material.
> 
> For instance there are people who use the kernel keyring to replace
> ssh-agent and thus *reduce* the attack surface they have for storing
> ssh keys:
> 
> https://blog.cloudflare.com/the-linux-kernel-key-retention-service-and-why-you-should-use-it-in-your-next-application/
>  
> The same thing could be done with gpg keys or the gnome keyring.

Eric has a correct standing given that the commit message does not have
motivation part at all. 

With a description of the problem that this patch is supposed to solve
this would be more meaningful to review.

BR, Jarkko


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