Re: [PATCH v4 2/2] KEYS: asymmetric: Copy sig and digest in public_key_verify_signature()

[Roberto Sassu]

On 12/27/2022 10:46 AM, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> Commit ac4e97abce9b8 ("scatterlist: sg_set_buf() argument must be in linear
> mapping") checks that both the signature and the digest reside in the
> linear mapping area.
>
> However, more recently commit ba14a194a434c ("fork: Add generic vmalloced
> stack support"), made it possible to move the stack in the vmalloc area,
> which is not contiguous, and thus not suitable for sg_set_buf() which needs
> adjacent pages.
>
> Always make a copy of the signature and digest in the same buffer used to
> store the key and its parameters, and pass them to sg_set_buf(). Prefer it
> to conditionally doing the copy if necessary, to keep the code simple. The
> buffer allocated with kmalloc() is in the linear mapping area.
>
> Cc: stable@xxxxxxxxxxxxxxx # 4.9.x
> Fixes: ba14a194a434 ("fork: Add generic vmalloced stack support")
> Link: https://lore.kernel.org/linux-integrity/Y4pIpxbjBdajymBJ@sol.localdomain/
> Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>   crypto/asymmetric_keys/public_key.c | 39 ++++++++++++++++-------------
>   1 file changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
> index 2f8352e88860..a479e32cb280 100644
> --- a/crypto/asymmetric_keys/public_key.c
> +++ b/crypto/asymmetric_keys/public_key.c
> @@ -360,9 +360,10 @@ int public_key_verify_signature(const struct public_key *pkey,
>   	struct crypto_wait cwait;
>   	struct crypto_akcipher *tfm;
>   	struct akcipher_request *req;
> -	struct scatterlist src_sg[2];
> +	struct scatterlist src_sg;
>   	char alg_name[CRYPTO_MAX_ALG_NAME];
> -	char *key, *ptr;
> +	char *buf, *ptr;
> +	size_t buf_len;
>   	int ret;
>   
>   	pr_devel("==>%s()\n", __func__);
> @@ -400,34 +401,38 @@ int public_key_verify_signature(const struct public_key *pkey,
>   	if (!req)
>   		goto error_free_tfm;
>   
> -	key = kmalloc(pkey->keylen + sizeof(u32) * 2 + pkey->paramlen,
> -		      GFP_KERNEL);
> -	if (!key)
> +	buf_len = max_t(size_t, pkey->keylen + sizeof(u32) * 2 + pkey->paramlen,
> +			sig->s_size + sig->digest_size);
> +
> +	buf = kmalloc(buf_len, GFP_KERNEL);
> +	if (!buf)
>   		goto error_free_req;
>   
> -	memcpy(key, pkey->key, pkey->keylen);
> -	ptr = key + pkey->keylen;
> +	memcpy(buf, pkey->key, pkey->keylen);
> +	ptr = buf + pkey->keylen;
>   	ptr = pkey_pack_u32(ptr, pkey->algo);
>   	ptr = pkey_pack_u32(ptr, pkey->paramlen);
>   	memcpy(ptr, pkey->params, pkey->paramlen);
>   
>   	if (pkey->key_is_private)
> -		ret = crypto_akcipher_set_priv_key(tfm, key, pkey->keylen);
> +		ret = crypto_akcipher_set_priv_key(tfm, buf, pkey->keylen);
>   	else
> -		ret = crypto_akcipher_set_pub_key(tfm, key, pkey->keylen);
> +		ret = crypto_akcipher_set_pub_key(tfm, buf, pkey->keylen);
>   	if (ret)
> -		goto error_free_key;
> +		goto error_free_buf;
>   
>   	if (strcmp(pkey->pkey_algo, "sm2") == 0 && sig->data_size) {
>   		ret = cert_sig_digest_update(sig, tfm);
>   		if (ret)
> -			goto error_free_key;
> +			goto error_free_buf;
>   	}
>   
> -	sg_init_table(src_sg, 2);
> -	sg_set_buf(&src_sg[0], sig->s, sig->s_size);
> -	sg_set_buf(&src_sg[1], sig->digest, sig->digest_size);
> -	akcipher_request_set_crypt(req, src_sg, NULL, sig->s_size,
> +	memcpy(buf, sig->s, sig->s_size);
> +	memcpy(buf + sig->s_size, sig->digest, sig->digest_size);
> +
> +	sg_init_table(&src_sg, 1);
> +	sg_set_buf(&src_sg, buf, sig->s_size + sig->digest_size);

Ops, didn't commit the changes. Will send a new version soon.

Roberto

> +	akcipher_request_set_crypt(req, &src_sg, NULL, sig->s_size,
>   				   sig->digest_size);
>   	crypto_init_wait(&cwait);
>   	akcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
> @@ -435,8 +440,8 @@ int public_key_verify_signature(const struct public_key *pkey,
>   				      crypto_req_done, &cwait);
>   	ret = crypto_wait_req(crypto_akcipher_verify(req), &cwait);
>   
> -error_free_key:
> -	kfree(key);
> +error_free_buf:
> +	kfree(buf);
>   error_free_req:
>   	akcipher_request_free(req);
>   error_free_tfm: