Re: [PATCH v3 7/7] fs: cifs: switch to RC4 library interface

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Jun 11, 2019 at 03:47:50PM +0200, Ard Biesheuvel wrote:
> The CIFS code uses the sync skcipher API to invoke the ecb(arc4) skcipher,
> of which only a single generic C code implementation exists. This means
> that going through all the trouble of using scatterlists etc buys us
> very little, and we're better off just invoking the arc4 library directly.
> 
> Cc: linux-cifs@vger.kernel.org
> Cc: Steve French <sfrench@samba.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  fs/cifs/Kconfig       |  2 +-
>  fs/cifs/cifsencrypt.c | 53 ++++++--------------
>  2 files changed, 16 insertions(+), 39 deletions(-)
> 
> diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
> index aae2b8b2adf5..523e9ea78a28 100644
> --- a/fs/cifs/Kconfig
> +++ b/fs/cifs/Kconfig
> @@ -10,7 +10,7 @@ config CIFS
>  	select CRYPTO_SHA512
>  	select CRYPTO_CMAC
>  	select CRYPTO_HMAC
> -	select CRYPTO_ARC4
> +	select CRYPTO_LIB_ARC4
>  	select CRYPTO_AEAD2
>  	select CRYPTO_CCM
>  	select CRYPTO_ECB

Since the "arc4" module is no longer needed, the

	MODULE_SOFTDEP("pre: arc4");

in fs/cifs/cifsfs.c should be removed too.

(Note that it doesn't need a soft dependency on libarc4 instead, since the cifs
module will link directly to it.)

> diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c
> index d2a05e46d6f5..3b7b5e83493d 100644
> --- a/fs/cifs/cifsencrypt.c
> +++ b/fs/cifs/cifsencrypt.c
> @@ -33,7 +33,8 @@
>  #include <linux/ctype.h>
>  #include <linux/random.h>
>  #include <linux/highmem.h>
> -#include <crypto/skcipher.h>
> +#include <linux/fips.h>
> +#include <crypto/arc4.h>
>  #include <crypto/aead.h>
>  
>  int __cifs_calc_signature(struct smb_rqst *rqst,
> @@ -772,11 +773,12 @@ setup_ntlmv2_rsp(struct cifs_ses *ses, const struct nls_table *nls_cp)
>  int
>  calc_seckey(struct cifs_ses *ses)
>  {
> -	int rc;
> -	struct crypto_skcipher *tfm_arc4;
> -	struct scatterlist sgin, sgout;
> -	struct skcipher_request *req;
> +	struct arc4_ctx *ctx_arc4;
>  	unsigned char *sec_key;
> +	int rc = 0;
> +
> +	if (fips_enabled)
> +		return -ENODEV;
>  
>  	sec_key = kmalloc(CIFS_SESS_KEY_SIZE, GFP_KERNEL);
>  	if (sec_key == NULL)

sec_key should be moved back to the stack now, basically reverting this commit:

	commit 5f4b55699aaff1028468e3f53853d781cdafedd6
	Author: Sachin Prabhu <sprabhu@redhat.com>
	Date:   Mon Oct 17 16:40:22 2016 -0400

	    CIFS: Fix BUG() in calc_seckey()

It was only moved to the heap because it had to go in a scatterlist.

> +	arc4_setkey(ctx_arc4, ses->auth_key.response, CIFS_SESS_KEY_SIZE);
> +	arc4_crypt(ctx_arc4, ses->ntlmssp->ciphertext, sec_key,
> +		   CIFS_CPHTXT_SIZE);
>  
>  	/* make secondary_key/nonce as session key */
>  	memcpy(ses->auth_key.response, sec_key, CIFS_SESS_KEY_SIZE);
>  	/* and make len as that of session key only */
>  	ses->auth_key.len = CIFS_SESS_KEY_SIZE;
>  
> -out_free_cipher:
> -	crypto_free_skcipher(tfm_arc4);
>  out:
> +	kfree(ctx_arc4);

Should be kzfree().

- Eric