[PATCH v2 1/1] s390/zcrypt: Fix and improve zcrypt reply message verification checks

[Harald Freudenberger <freude@linux.ibm.com>]

Add or improve checks related to buffer sizes and reply sizes to the
handling of replies from the crypto cards for CCA, EP11 (AP message
type 6) and ICA (AP type 50) messages. The verification code related
to reply field length was not designed well and thus firmware
deficiencies could lead to unexpected behavior in the zcrypt device
driver. Thus improve the code to more closely inspect especially
length fields at message replies.

Add length validation before accessing reply message structures in
zcrypt_msgtype6_receive(), zcrypt_msgtype6_receive_ep11(), and
zcrypt_msgtype50_receive() to prevent out-of-bounds reads and
potential kernel memory disclosure.

Also rework these three functions to validate reply lengths more
carefully before copying data back into the request buffer. Use size_t
for length calculations, reject inconsistent reply sizes, and add
defensive handling for short invalid replies. For XCRB replies,
validate both reply segments and derive the effective message length
from the covered range instead of trusting only the second segment.

Fixes: 3b6245fd303f ("s390/zcrypt: Separate msgtype implementation from card modules.")
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Cc: stable@vger.kernel.org
---
 drivers/s390/crypto/zcrypt_msgtype50.c |  40 +++++--
 drivers/s390/crypto/zcrypt_msgtype6.c  | 160 +++++++++++++++++--------
 2 files changed, 136 insertions(+), 64 deletions(-)

diff --git a/drivers/s390/crypto/zcrypt_msgtype50.c b/drivers/s390/crypto/zcrypt_msgtype50.c
index d6fc2d8e7fad..80c447ea2d83 100644
--- a/drivers/s390/crypto/zcrypt_msgtype50.c
+++ b/drivers/s390/crypto/zcrypt_msgtype50.c
@@ -416,26 +416,40 @@ static void zcrypt_msgtype50_receive(struct ap_queue *aq,
 		.reply_code = REP82_ERROR_MACHINE_FAILURE,
 	};
 	struct type80_hdr *t80h;
-	int len;
+	size_t len;
 
 	/* Copy the reply message to the request message buffer. */
 	if (!reply)
 		goto out;	/* ap_msg->rc indicates the error */
+
 	t80h = reply->msg;
-	if (t80h->type == TYPE80_RSP_CODE) {
-		len = t80h->len;
-		if (len > reply->bufsize || len > msg->bufsize ||
-		    len != reply->len) {
-			pr_debug("len mismatch => EMSGSIZE\n");
-			msg->rc = -EMSGSIZE;
-			goto out;
-		}
-		memcpy(msg->msg, reply->msg, len);
-		msg->len = len;
-	} else {
-		memcpy(msg->msg, reply->msg, sizeof(error_reply));
+
+	if (reply->len < sizeof(*t80h) ||
+	    t80h->type != TYPE80_RSP_CODE) {
+		if (reply->len < sizeof(error_reply))
+			memcpy(msg->msg, &error_reply, sizeof(error_reply));
+		else
+			memcpy(msg->msg, reply->msg, sizeof(error_reply));
 		msg->len = sizeof(error_reply);
+		goto out;
+	}
+
+	len = t80h->len;
+	if (len != reply->len) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu rpl.len %zu mismatch, msg.rc=%d\n",
+			 len, reply->len, msg->rc);
+		goto out;
 	}
+	if (len > reply->bufsize || len > msg->bufsize) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu exceeds buf %zu/%zu, msg.rc=%d\n",
+			 len, reply->bufsize, msg->bufsize, msg->rc);
+		goto out;
+	}
+	memcpy(msg->msg, reply->msg, len);
+	msg->len = len;
+
 out:
 	complete(&msg->response.work);
 }
diff --git a/drivers/s390/crypto/zcrypt_msgtype6.c b/drivers/s390/crypto/zcrypt_msgtype6.c
index 3df1d676de5d..b53801b0a971 100644
--- a/drivers/s390/crypto/zcrypt_msgtype6.c
+++ b/drivers/s390/crypto/zcrypt_msgtype6.c
@@ -766,6 +766,13 @@ static int convert_type86_rng(struct zcrypt_queue *zq,
 
 	if (msg->cprbx.ccp_rtcode != 0 || msg->cprbx.ccp_rscode != 0)
 		return -EINVAL;
+	/*
+	 * Note that offset2 and count2 have already been checked in
+	 * zcrypt_msgtype6_receive(). So only check for not exceeding
+	 * the hard coded rng buffer size.
+	 */
+	if (msg->fmt2.count2 > ZCRYPT_RNG_BUFFER_SIZE)
+		return -EMSGSIZE;
 	memcpy(buffer, data + msg->fmt2.offset2, msg->fmt2.count2);
 	return msg->fmt2.count2;
 }
@@ -928,48 +935,80 @@ static void zcrypt_msgtype6_receive(struct ap_queue *aq,
 	};
 	struct ap_response_type *resp_type = &msg->response;
 	struct type86x_reply *t86r;
-	int len;
+	size_t minlen, len;
 
 	/* Copy the reply message to the request message buffer. */
 	if (!reply)
 		goto out;	/* ap_msg->rc indicates the error */
+
 	t86r = reply->msg;
-	if (t86r->hdr.type == TYPE86_RSP_CODE &&
-	    t86r->cprbx.cprb_ver_id == 0x02) {
-		switch (resp_type->type) {
-		case CEXXC_RESPONSE_TYPE_ICA:
-			len = sizeof(struct type86x_reply) + t86r->length;
-			if (len > reply->bufsize || len > msg->bufsize ||
-			    len != reply->len) {
-				pr_debug("len mismatch => EMSGSIZE\n");
-				msg->rc = -EMSGSIZE;
-				goto out;
-			}
-			memcpy(msg->msg, reply->msg, len);
-			msg->len = len;
-			break;
-		case CEXXC_RESPONSE_TYPE_XCRB:
-			if (t86r->fmt2.count2)
-				len = t86r->fmt2.offset2 + t86r->fmt2.count2;
-			else
-				len = t86r->fmt2.offset1 + t86r->fmt2.count1;
-			if (len > reply->bufsize || len > msg->bufsize ||
-			    len != reply->len) {
-				pr_debug("len mismatch => EMSGSIZE\n");
+	minlen = sizeof(t86r->hdr) + sizeof(t86r->fmt2) +
+		offsetof(struct CPRBX, cprb_ver_id) +
+		sizeof(t86r->cprbx.cprb_ver_id);
+
+	if (reply->len < minlen ||
+	    t86r->hdr.type != TYPE86_RSP_CODE ||
+	    t86r->cprbx.cprb_ver_id != 0x02) {
+		if (reply->len < sizeof(error_reply))
+			memcpy(msg->msg, &error_reply, sizeof(error_reply));
+		else
+			memcpy(msg->msg, reply->msg, sizeof(error_reply));
+		msg->len = sizeof(error_reply);
+		goto out;
+	}
+
+	switch (resp_type->type) {
+	case CEXXC_RESPONSE_TYPE_ICA:
+		if (reply->len < sizeof(struct type86x_reply)) {
+			msg->rc = -EMSGSIZE;
+			pr_debug("rpl.len %zu < struct type86_reply, msg.rc=%d\n",
+				 reply->len, msg->rc);
+			goto out;
+		}
+		len = sizeof(struct type86x_reply) + (size_t)t86r->length;
+		break;
+	case CEXXC_RESPONSE_TYPE_XCRB:
+		len = (size_t)t86r->fmt2.offset1 + (size_t)t86r->fmt2.count1;
+		if (len > reply->len) {
+			msg->rc = -EMSGSIZE;
+			pr_debug("offset1 %u count1 %u rpl.len %zu mismatch, msg.rc=%d\n",
+				 t86r->fmt2.offset1, t86r->fmt2.count1,
+				 reply->len, msg->rc);
+			goto out;
+		}
+		if (t86r->fmt2.count2) {
+			len = (size_t)t86r->fmt2.offset2 +
+				(size_t)t86r->fmt2.count2;
+			if (len > reply->len) {
 				msg->rc = -EMSGSIZE;
+				pr_debug("offset2 %u count2 %u rpl.len %zu mismatch, msg.rc=%d\n",
+					 t86r->fmt2.offset2, t86r->fmt2.count2,
+					 reply->len, msg->rc);
 				goto out;
 			}
-			memcpy(msg->msg, reply->msg, len);
-			msg->len = len;
-			break;
-		default:
-			memcpy(msg->msg, &error_reply, sizeof(error_reply));
-			msg->len = sizeof(error_reply);
 		}
-	} else {
-		memcpy(msg->msg, reply->msg, sizeof(error_reply));
+		break;
+	default:
+		memcpy(msg->msg, &error_reply, sizeof(error_reply));
 		msg->len = sizeof(error_reply);
+		goto out;
 	}
+
+	if (len != reply->len) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu rpl.len %zu mismatch, msg.rc=%d\n",
+			 len, reply->len, msg->rc);
+		goto out;
+	}
+	if (len > reply->bufsize || len > msg->bufsize) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu exceeds buf %zu/%zu, msg.rc=%d\n",
+			 len, reply->bufsize, msg->bufsize, msg->rc);
+		goto out;
+	}
+	memcpy(msg->msg, reply->msg, len);
+	msg->len = len;
+
 out:
 	complete(&resp_type->work);
 }
@@ -992,34 +1031,53 @@ static void zcrypt_msgtype6_receive_ep11(struct ap_queue *aq,
 	};
 	struct ap_response_type *resp_type = &msg->response;
 	struct type86_ep11_reply *t86r;
-	int len;
+	size_t minlen, len;
 
 	/* Copy the reply message to the request message buffer. */
 	if (!reply)
 		goto out;	/* ap_msg->rc indicates the error */
+
 	t86r = reply->msg;
-	if (t86r->hdr.type == TYPE86_RSP_CODE &&
-	    t86r->cprbx.cprb_ver_id == 0x04) {
-		switch (resp_type->type) {
-		case CEXXC_RESPONSE_TYPE_EP11:
-			len = t86r->fmt2.offset1 + t86r->fmt2.count1;
-			if (len > reply->bufsize || len > msg->bufsize ||
-			    len != reply->len) {
-				pr_debug("len mismatch => EMSGSIZE\n");
-				msg->rc = -EMSGSIZE;
-				goto out;
-			}
-			memcpy(msg->msg, reply->msg, len);
-			msg->len = len;
-			break;
-		default:
+	minlen = sizeof(t86r->hdr) + sizeof(t86r->fmt2) +
+		offsetof(struct ep11_cprb, cprb_ver_id) +
+		sizeof(t86r->cprbx.cprb_ver_id);
+
+	if (reply->len < minlen ||
+	    t86r->hdr.type != TYPE86_RSP_CODE ||
+	    t86r->cprbx.cprb_ver_id != 0x04) {
+		if (reply->len < sizeof(error_reply))
 			memcpy(msg->msg, &error_reply, sizeof(error_reply));
-			msg->len = sizeof(error_reply);
-		}
-	} else {
-		memcpy(msg->msg, reply->msg, sizeof(error_reply));
+		else
+			memcpy(msg->msg, reply->msg, sizeof(error_reply));
 		msg->len = sizeof(error_reply);
+		goto out;
 	}
+
+	switch (resp_type->type) {
+	case CEXXC_RESPONSE_TYPE_EP11:
+		len = (size_t)t86r->fmt2.offset1 + (size_t)t86r->fmt2.count1;
+		break;
+	default:
+		memcpy(msg->msg, &error_reply, sizeof(error_reply));
+		msg->len = sizeof(error_reply);
+		goto out;
+	}
+
+	if (len != reply->len) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu rpl.len %zu mismatch, msg.rc=%d\n",
+			 len, reply->len, msg->rc);
+		goto out;
+	}
+	if (len > reply->bufsize || len > msg->bufsize) {
+		msg->rc = -EMSGSIZE;
+		pr_debug("len %zu exceeds buf %zu/%zu, msg.rc=%d\n",
+			 len, reply->bufsize, msg->bufsize, msg->rc);
+		goto out;
+	}
+	memcpy(msg->msg, reply->msg, len);
+	msg->len = len;
+
 out:
 	complete(&resp_type->work);
 }
-- 
2.43.0