block: take care not to overflow when calculating total iov length

Reported-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/scsi_ioctl.c

@@ -321,33 +321,47 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
 	if (hdr->iovec_count) {
 		const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
 		size_t iov_data_len;
-		struct sg_iovec *iov;
+		struct sg_iovec *sg_iov;
+		struct iovec *iov;
+		int i;
 
-		iov = kmalloc(size, GFP_KERNEL);
-		if (!iov) {
+		sg_iov = kmalloc(size, GFP_KERNEL);
+		if (!sg_iov) {
 			ret = -ENOMEM;
 			goto out;
 		}
 
-		if (copy_from_user(iov, hdr->dxferp, size)) {
-			kfree(iov);
+		if (copy_from_user(sg_iov, hdr->dxferp, size)) {
+			kfree(sg_iov);
 			ret = -EFAULT;
 			goto out;
 		}
 
+		/*
+		 * Sum up the vecs, making sure they don't overflow
+		 */
+		iov = (struct iovec *) sg_iov;
+		iov_data_len = 0;
+		for (i = 0; i < hdr->iovec_count; i++) {
+			if (iov_data_len + iov[i].iov_len < iov_data_len) {
+				kfree(sg_iov);
+				ret = -EINVAL;
+				goto out;
+			}
+			iov_data_len += iov[i].iov_len;
+		}
+
 		/* SG_IO howto says that the shorter of the two wins */
-		iov_data_len = iov_length((struct iovec *)iov,
-					  hdr->iovec_count);
 		if (hdr->dxfer_len < iov_data_len) {
-			hdr->iovec_count = iov_shorten((struct iovec *)iov,
+			hdr->iovec_count = iov_shorten(iov,
 						       hdr->iovec_count,
 						       hdr->dxfer_len);
 			iov_data_len = hdr->dxfer_len;
 		}
 
-		ret = blk_rq_map_user_iov(q, rq, NULL, iov, hdr->iovec_count,
+		ret = blk_rq_map_user_iov(q, rq, NULL, sg_iov, hdr->iovec_count,
 					  iov_data_len, GFP_KERNEL);
-		kfree(iov);
+		kfree(sg_iov);
 	} else if (hdr->dxfer_len)
 		ret = blk_rq_map_user(q, rq, NULL, hdr->dxferp, hdr->dxfer_len,
 				      GFP_KERNEL);