Re: [PATCH] fscrypt: verify that the crypto_skcipher has the correct ivsize

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Dec 09, 2019 at 12:39:18PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> As a sanity check, verify that the allocated crypto_skcipher actually
> has the ivsize that fscrypt is assuming it has.  This will always be the
> case unless there's a bug.  But if there ever is such a bug (e.g. like
> there was in earlier versions of the ESSIV conversion patch [1]) it's
> preferable for it to be immediately obvious, and not rely on the
> ciphertext verification tests failing due to uninitialized IV bytes.
> 
> [1] https://lkml.kernel.org/linux-crypto/20190702215517.GA69157@gmail.com/
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  fs/crypto/keysetup.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
> index c9f4fe955971f..39fdea79e912f 100644
> --- a/fs/crypto/keysetup.c
> +++ b/fs/crypto/keysetup.c
> @@ -91,6 +91,10 @@ struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
>  		pr_info("fscrypt: %s using implementation \"%s\"\n",
>  			mode->friendly_name, crypto_skcipher_driver_name(tfm));
>  	}
> +	if (WARN_ON(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
> +		err = -EINVAL;
> +		goto err_free_tfm;
> +	}
>  	crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
>  	err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
>  	if (err)
> -- 
> 2.24.0.393.g34dc348eaf-goog
> 

Applied to fscrypt.git#master for 5.6.

- Eric