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1e562deace
A sig_alg backend has just been introduced with the intent of moving all
asymmetric sign/verify algorithms to it one by one.
Migrate the sign/verify operations from rsa-pkcs1pad.c to a separate
rsassa-pkcs1.c which uses the new backend.
Consequently there are now two templates which build on the "rsa"
akcipher_alg:
* The existing "pkcs1pad" template, which is instantiated as an
akcipher_instance and retains the encrypt/decrypt operations of
RSAES-PKCS1-v1_5 (RFC 8017 sec 7.2).
* The new "pkcs1" template, which is instantiated as a sig_instance
and contains the sign/verify operations of RSASSA-PKCS1-v1_5
(RFC 8017 sec 8.2).
In a separate step, rsa-pkcs1pad.c could optionally be renamed to
rsaes-pkcs1.c for clarity. Additional "oaep" and "pss" templates
could be added for RSAES-OAEP and RSASSA-PSS.
Note that it's currently allowed to allocate a "pkcs1pad(rsa)" transform
without specifying a hash algorithm. That makes sense if the transform
is only used for encrypt/decrypt and continues to be supported. But for
sign/verify, such transforms previously did not insert the Full Hash
Prefix into the padding. The resulting message encoding was incompliant
with EMSA-PKCS1-v1_5 (RFC 8017 sec 9.2) and therefore nonsensical.
From here on in, it is no longer allowed to allocate a transform without
specifying a hash algorithm if the transform is used for sign/verify
operations. This simplifies the code because the insertion of the Full
Hash Prefix is no longer optional, so various "if (digest_info)" clauses
can be removed.
There has been a previous attempt to forbid transform allocation without
specifying a hash algorithm, namely by commit c0d20d22e0ad ("crypto:
rsa-pkcs1pad - Require hash to be present"). It had to be rolled back
with commit b3a8c8a5ebb5 ("crypto: rsa-pkcs1pad: Allow hash to be
optional [ver #2]"), presumably because it broke allocation of a
transform which was solely used for encrypt/decrypt, not sign/verify.
Avoid such breakage by allowing transform allocation for encrypt/decrypt
with and without specifying a hash algorithm (and simply ignoring the
hash algorithm in the former case).
So again, specifying a hash algorithm is now mandatory for sign/verify,
but optional and ignored for encrypt/decrypt.
The new sig_alg API uses kernel buffers instead of sglists, which
avoids the overhead of copying signature and digest from sglists back
into kernel buffers. rsassa-pkcs1.c is thus simplified quite a bit.
sig_alg is always synchronous, whereas the underlying "rsa" akcipher_alg
may be asynchronous. So await the result of the akcipher_alg, similar
to crypto_akcipher_sync_{en,de}crypt().
As part of the migration, rename "rsa_digest_info" to "hash_prefix" to
adhere to the spec language in RFC 9580. Otherwise keep the code
unmodified wherever possible to ease reviewing and bisecting. Leave
several simplification and hardening opportunities to separate commits.
rsassa-pkcs1.c uses modern __free() syntax for allocation of buffers
which need to be freed by kfree_sensitive(), hence a DEFINE_FREE()
clause for kfree_sensitive() is introduced herein as a byproduct.
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.