KEYS: asymmetric: Copy sig and digest in public_key_verify_signature()

Commit ac4e97a ("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 ba14a19 ("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_init_one(). 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@vger.kernel.org # 4.9.x
Fixes: ba14a19 ("fork: Add generic vmalloced stack support")
Link: https://lore.kernel.org/linux-integrity/Y4pIpxbjBdajymBJ@sol.localdomain/
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>

crypto/asymmetric_keys/public_key.c

@@ -380,9 +380,10 @@ 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__);
@@ -420,43 +421,46 @@ 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_one(&src_sg, buf, sig->s_size + sig->digest_size);
+	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 |
 				      CRYPTO_TFM_REQ_MAY_SLEEP,
 				      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: