KEYS: asymmetric: Copy sig and digest in public_key_verify_signature()

[stefanberger]

Commit ac4e97a ("scatterlist: sg_set_buf() argument must be in linear mapping") checks that both the signature and the digest reside in the linear mapping area.

However, more recently commit ba14a19 ("fork: Add generic vmalloced stack support") made it possible to move the stack in the vmalloc area, which is not contiguous, and thus not suitable for sg_set_buf() which needs adjacent pages.

Always make a copy of the signature and digest in the same buffer used to store the key and its parameters, and pass them to sg_init_one(). Prefer it to conditionally doing the copy if necessary, to keep the code simple. The buffer allocated with kmalloc() is in the linear mapping area.

Cc: stable@vger.kernel.org # 4.9.x
Fixes: ba14a19 ("fork: Add generic vmalloced stack support")
Link: https://lore.kernel.org/linux-integrity/Y4pIpxbjBdajymBJ@sol.localdomain/
Suggested-by: Eric Biggers ebiggers@kernel.org

Reviewed-by: Eric Biggers ebiggers@google.com
Tested-by: Stefan Berger stefanb@linux.ibm.com

[stefanberger]

This particular patch has now been merged upstream: torvalds@c3d03e8

I need this patch for proper EVM signature enforcement and will drop it from my OpenBMC series of patches once the OpenBMC Linux build includes this patch. I have been carrying this patch here lately: https://gerrit.openbmc.org/c/openbmc/openbmc/+/63909