Re: [PATCH v5 7/7] fs: cifs: switch to RC4 library interface

[Steve French <smfrench@gmail.com>]

Acked-by: Steve French <stfrench@microsoft.com>

On Wed, Jun 12, 2019 at 1:06 PM Ard Biesheuvel
<ard.biesheuvel@linaro.org> 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.
>
> This also reverts commit 5f4b55699aaf ("CIFS: Fix BUG() in calc_seckey()"),
> since it is no longer necessary to allocate sec_key on the heap.
>
> 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 | 62 +++++---------------
>  fs/cifs/cifsfs.c      |  1 -
>  3 files changed, 17 insertions(+), 48 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
> diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c
> index d2a05e46d6f5..97b7497c13ef 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,
> @@ -772,63 +773,32 @@ 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;
> -       unsigned char *sec_key;
> +       unsigned char sec_key[CIFS_SESS_KEY_SIZE]; /* a nonce */
> +       struct arc4_ctx *ctx_arc4;
>
> -       sec_key = kmalloc(CIFS_SESS_KEY_SIZE, GFP_KERNEL);
> -       if (sec_key == NULL)
> -               return -ENOMEM;
> +       if (fips_enabled)
> +               return -ENODEV;
>
>         get_random_bytes(sec_key, CIFS_SESS_KEY_SIZE);
>
> -       tfm_arc4 = crypto_alloc_skcipher("ecb(arc4)", 0, CRYPTO_ALG_ASYNC);
> -       if (IS_ERR(tfm_arc4)) {
> -               rc = PTR_ERR(tfm_arc4);
> -               cifs_dbg(VFS, "could not allocate crypto API arc4\n");
> -               goto out;
> -       }
> -
> -       rc = crypto_skcipher_setkey(tfm_arc4, ses->auth_key.response,
> -                                       CIFS_SESS_KEY_SIZE);
> -       if (rc) {
> -               cifs_dbg(VFS, "%s: Could not set response as a key\n",
> -                        __func__);
> -               goto out_free_cipher;
> -       }
> -
> -       req = skcipher_request_alloc(tfm_arc4, GFP_KERNEL);
> -       if (!req) {
> -               rc = -ENOMEM;
> -               cifs_dbg(VFS, "could not allocate crypto API arc4 request\n");
> -               goto out_free_cipher;
> +       ctx_arc4 = kmalloc(sizeof(*ctx_arc4), GFP_KERNEL);
> +       if (!ctx_arc4) {
> +               cifs_dbg(VFS, "could not allocate arc4 context\n");
> +               return -ENOMEM;
>         }
>
> -       sg_init_one(&sgin, sec_key, CIFS_SESS_KEY_SIZE);
> -       sg_init_one(&sgout, ses->ntlmssp->ciphertext, CIFS_CPHTXT_SIZE);
> -
> -       skcipher_request_set_callback(req, 0, NULL, NULL);
> -       skcipher_request_set_crypt(req, &sgin, &sgout, CIFS_CPHTXT_SIZE, NULL);
> -
> -       rc = crypto_skcipher_encrypt(req);
> -       skcipher_request_free(req);
> -       if (rc) {
> -               cifs_dbg(VFS, "could not encrypt session key rc: %d\n", rc);
> -               goto out_free_cipher;
> -       }
> +       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(sec_key);
> -       return rc;
> +       memzero_explicit(sec_key, CIFS_SESS_KEY_SIZE);
> +       kzfree(ctx_arc4);
> +       return 0;
>  }
>
>  void
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index f5fcd6360056..e55afaf9e5a3 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -1590,7 +1590,6 @@ MODULE_DESCRIPTION
>         ("VFS to access SMB3 servers e.g. Samba, Macs, Azure and Windows (and "
>         "also older servers complying with the SNIA CIFS Specification)");
>  MODULE_VERSION(CIFS_VERSION);
> -MODULE_SOFTDEP("pre: arc4");
>  MODULE_SOFTDEP("pre: des");
>  MODULE_SOFTDEP("pre: ecb");
>  MODULE_SOFTDEP("pre: hmac");
> --
> 2.20.1
>


-- 
Thanks,

Steve