mei: fix possible integer overflow issue

There is a possible integer overflow following by a buffer overflow
when accumulating messages coming from the FW to compose a full payload.
Occurrence of wrap around has to be prevented for next message size
calculation.
For unsigned integer the addition overflow has occurred when the
result is smaller than one of the arguments.
To simplify the fix, the types of buf.size and buf_idx are set to the
same width, namely size_t also to be aligned with the type of length
parameter in file read/write ops.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/amthif.c

@@ -195,9 +195,8 @@ int mei_amthif_read(struct mei_device *dev, struct file *file,
 		 * remove message from deletion list
 		 */
 
-	dev_dbg(dev->dev, "amthif cb->buf size - %d\n",
-	    cb->buf.size);
-	dev_dbg(dev->dev, "amthif cb->buf_idx - %lu\n", cb->buf_idx);
+	dev_dbg(dev->dev, "amthif cb->buf.size - %zd cb->buf_idx - %zd\n",
+		cb->buf.size, cb->buf_idx);
 
 	/* length is being truncated to PAGE_SIZE, however,
 	 * the buf_idx may point beyond */

drivers/misc/mei/client.c

@@ -1569,7 +1569,7 @@ int mei_cl_irq_write(struct mei_cl *cl, struct mei_cl_cb *cb,
 		return 0;
 	}
 
-	cl_dbg(dev, cl, "buf: size = %d idx = %lu\n",
+	cl_dbg(dev, cl, "buf: size = %zd idx = %zd\n",
 			cb->buf.size, cb->buf_idx);
 
 	rets = mei_write_message(dev, &mei_hdr, buf->data + cb->buf_idx);

drivers/misc/mei/interrupt.c

@@ -104,6 +104,7 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 	struct mei_device *dev = cl->dev;
 	struct mei_cl_cb *cb;
 	unsigned char *buffer = NULL;
+	size_t buf_sz;
 
 	cb = list_first_entry_or_null(&cl->rd_pending, struct mei_cl_cb, list);
 	if (!cb) {
@@ -124,11 +125,21 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 		goto out;
 	}
 
-	if (cb->buf.size < mei_hdr->length + cb->buf_idx) {
-		cl_dbg(dev, cl, "message overflow. size %d len %d idx %ld\n",
+	buf_sz = mei_hdr->length + cb->buf_idx;
+	/* catch for integer overflow */
+	if (buf_sz < cb->buf_idx) {
+		cl_err(dev, cl, "message is too big len %d idx %ld\n",
+		       mei_hdr->length, cb->buf_idx);
+
+		list_move_tail(&cb->list, &complete_list->list);
+		cb->status = -EMSGSIZE;
+		goto out;
+	}
+
+	if (cb->buf.size < buf_sz) {
+		cl_dbg(dev, cl, "message overflow. size %zd len %d idx %zd\n",
 			cb->buf.size, mei_hdr->length, cb->buf_idx);
-		buffer = krealloc(cb->buf.data, mei_hdr->length + cb->buf_idx,
-				  GFP_KERNEL);
+		buffer = krealloc(cb->buf.data, buf_sz, GFP_KERNEL);
 
 		if (!buffer) {
 			cb->status = -ENOMEM;
@@ -136,7 +147,7 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 			goto out;
 		}
 		cb->buf.data = buffer;
-		cb->buf.size = mei_hdr->length + cb->buf_idx;
+		cb->buf.size = buf_sz;
 	}
 
 	buffer = cb->buf.data + cb->buf_idx;

drivers/misc/mei/main.c

@@ -226,7 +226,7 @@ static ssize_t mei_read(struct file *file, char __user *ubuf,
 		goto free;
 	}
 
-	cl_dbg(dev, cl, "buf.size = %d buf.idx = %ld offset = %lld\n",
+	cl_dbg(dev, cl, "buf.size = %zd buf.idx = %zd offset = %lld\n",
 	       cb->buf.size, cb->buf_idx, *offset);
 	if (*offset >= cb->buf_idx) {
 		rets = 0;
@@ -245,7 +245,8 @@ static ssize_t mei_read(struct file *file, char __user *ubuf,
 
 	rets = length;
 	*offset += length;
-	if ((unsigned long)*offset < cb->buf_idx)
+	/* not all data was read, keep the cb */
+	if (*offset < cb->buf_idx)
 		goto out;
 
 free:

drivers/misc/mei/mei_dev.h

@@ -126,7 +126,7 @@ enum mei_cb_file_ops {
  * Intel MEI message data struct
  */
 struct mei_msg_data {
-	u32 size;
+	size_t size;
 	unsigned char *data;
 };
 
@@ -190,7 +190,7 @@ struct mei_cl_cb {
 	struct mei_cl *cl;
 	enum mei_cb_file_ops fop_type;
 	struct mei_msg_data buf;
-	unsigned long buf_idx;
+	size_t buf_idx;
 	unsigned long read_time;
 	struct file *file_object;
 	int status;