s390/zcrypt: add copy_from_user length plausibility checks

There have been identified some places in the zcrypt
device driver where copy_from_user() is called but the
length value is not explicitly checked.

So now some plausibility checks and comments have been
introduced there.
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/crypto/zcrypt_cca_key.h

@@ -99,7 +99,7 @@ struct cca_pvt_ext_CRT_sec {
  * @mex: pointer to user input data
  * @p: pointer to memory area for the key
  *
- * Returns the size of the key area or -EFAULT
+ * Returns the size of the key area or negative errno value.
  */
 static inline int zcrypt_type6_mex_key_en(struct ica_rsa_modexpo *mex, void *p)
 {
@@ -118,6 +118,15 @@ static inline int zcrypt_type6_mex_key_en(struct ica_rsa_modexpo *mex, void *p)
 	unsigned char *temp;
 	int i;
 
+	/*
+	 * The inputdatalength was a selection criteria in the dispatching
+	 * function zcrypt_rsa_modexpo(). However, do a plausibility check
+	 * here to make sure the following copy_from_user() can't be utilized
+	 * to compromise the system.
+	 */
+	if (WARN_ON_ONCE(mex->inputdatalength > 512))
+		return -EINVAL;
+
 	memset(key, 0, sizeof(*key));
 
 	key->pubHdr = static_pub_hdr;
@@ -178,6 +187,15 @@ static inline int zcrypt_type6_crt_key(struct ica_rsa_modexpo_crt *crt, void *p)
 	struct cca_public_sec *pub;
 	int short_len, long_len, pad_len, key_len, size;
 
+	/*
+	 * The inputdatalength was a selection criteria in the dispatching
+	 * function zcrypt_rsa_crt(). However, do a plausibility check
+	 * here to make sure the following copy_from_user() can't be utilized
+	 * to compromise the system.
+	 */
+	if (WARN_ON_ONCE(crt->inputdatalength > 512))
+		return -EINVAL;
+
 	memset(key, 0, sizeof(*key));
 
 	short_len = (crt->inputdatalength + 1) / 2;

drivers/s390/crypto/zcrypt_msgtype6.c

@@ -246,7 +246,7 @@ int speed_idx_ep11(int req_type)
  * @ap_msg: pointer to AP message
  * @mex: pointer to user input data
  *
- * Returns 0 on success or -EFAULT.
+ * Returns 0 on success or negative errno value.
  */
 static int ICAMEX_msg_to_type6MEX_msgX(struct zcrypt_queue *zq,
 				       struct ap_message *ap_msg,
@@ -272,6 +272,14 @@ static int ICAMEX_msg_to_type6MEX_msgX(struct zcrypt_queue *zq,
 	} __packed * msg = ap_msg->message;
 	int size;
 
+	/*
+	 * The inputdatalength was a selection criteria in the dispatching
+	 * function zcrypt_rsa_modexpo(). However, make sure the following
+	 * copy_from_user() never exceeds the allocated buffer space.
+	 */
+	if (WARN_ON_ONCE(mex->inputdatalength > PAGE_SIZE))
+		return -EINVAL;
+
 	/* VUD.ciphertext */
 	msg->length = mex->inputdatalength + 2;
 	if (copy_from_user(msg->text, mex->inputdata, mex->inputdatalength))
@@ -307,7 +315,7 @@ static int ICAMEX_msg_to_type6MEX_msgX(struct zcrypt_queue *zq,
  * @ap_msg: pointer to AP message
  * @crt: pointer to user input data
  *
- * Returns 0 on success or -EFAULT.
+ * Returns 0 on success or negative errno value.
  */
 static int ICACRT_msg_to_type6CRT_msgX(struct zcrypt_queue *zq,
 				       struct ap_message *ap_msg,
@@ -334,6 +342,14 @@ static int ICACRT_msg_to_type6CRT_msgX(struct zcrypt_queue *zq,
 	} __packed * msg = ap_msg->message;
 	int size;
 
+	/*
+	 * The inputdatalength was a selection criteria in the dispatching
+	 * function zcrypt_rsa_crt(). However, make sure the following
+	 * copy_from_user() never exceeds the allocated buffer space.
+	 */
+	if (WARN_ON_ONCE(crt->inputdatalength > PAGE_SIZE))
+		return -EINVAL;
+
 	/* VUD.ciphertext */
 	msg->length = crt->inputdatalength + 2;
 	if (copy_from_user(msg->text, crt->inputdata, crt->inputdatalength))