block: fix SG_[GS]ET_RESERVED_SIZE ioctl when max_sectors is huge

SG_GET_RESERVED_SIZE and SG_SET_RESERVED_SIZE ioctls access a reserved
buffer in bytes as int type.  The value needs to be capped at the request
queue's max_sectors.  But integer overflow is not correctly handled in
the calculation when converting max_sectors from sectors to bytes.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: linux-scsi@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/scsi_ioctl.c

@@ -82,9 +82,18 @@ static int sg_set_timeout(struct request_queue *q, int __user *p)
 	return err;
 }
 
+static int max_sectors_bytes(struct request_queue *q)
+{
+	unsigned int max_sectors = queue_max_sectors(q);
+
+	max_sectors = min_t(unsigned int, max_sectors, INT_MAX >> 9);
+
+	return max_sectors << 9;
+}
+
 static int sg_get_reserved_size(struct request_queue *q, int __user *p)
 {
-	unsigned val = min(q->sg_reserved_size, queue_max_sectors(q) << 9);
+	int val = min_t(int, q->sg_reserved_size, max_sectors_bytes(q));
 
 	return put_user(val, p);
 }
@@ -98,10 +107,8 @@ static int sg_set_reserved_size(struct request_queue *q, int __user *p)
 
 	if (size < 0)
 		return -EINVAL;
-	if (size > (queue_max_sectors(q) << 9))
-		size = queue_max_sectors(q) << 9;
 
-	q->sg_reserved_size = size;
+	q->sg_reserved_size = min(size, max_sectors_bytes(q));
 	return 0;
 }