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From:   =?UTF-8?B?T25kcmVqIE1vc27DocSNZWs=?= <omosnacek@gmail.com>
Date:   Tue, 21 Apr 2020 10:08:14 +0200
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Subject: libkcapi tests are failing on kernels 5.5+
To:     linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Stephan Mueller <smueller@chronox.de>
Cc:     Sahana Prasad <saprasad@redhat.com>, Tomas Mraz <tmraz@redhat.com>,
        Ard Biesheuvel <ardb@kernel.org>
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Hi all,

the libkcapi [1] tests are failing on kernels 5.5-rc1 and above [2].
All encryption/decryption tests that use 'ctr(aes)' and a message size
that is not a multiple of 16 fail due to kcapi-enc returning different
output than expected.

It seems that it started with:
commit 5b0fe9552336338acb52756daf65dd7a4eeca73f
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date:   Tue Sep 10 11:42:05 2019 +1000

    crypto: algif_skcipher - Use chunksize instead of blocksize

Reverting the above commit makes the tests pass again.

Here is a one-line reproducer:
head -c 257 /dev/zero | kcapi-enc -vvv --pbkdfiter 1 -p "passwd" -s
"123" -e -c "ctr(aes)" --iv "0123456789abcdef0123456789abcdef"
>/dev/null

Output without revert:
[...]
libkcapi - Debug: AF_ALG: recvmsg syscall returned 256
kcapi-enc - Verbose: Removal of padding disabled
kcapi-enc - Verbose: 256 bytes of ciphertext created

Output with the revert and on older kernels:
[...]
libkcapi - Debug: AF_ALG: recvmsg syscall returned 257
kcapi-enc - Verbose: Removal of padding disabled
kcapi-enc - Verbose: 257 bytes of ciphertext created

I'm not familiar with the code in question, so I'm not sure if this is
a kernel bug or whether the change just exposed a bug in libkcapi.

Stephan, Herbert, can you please have a look?

Thanks,

Ondrej

[1] https://github.com/smuellerDD/libkcapi
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1826022