block: fix BLKSECTGET ioctl when max_sectors is greater than USHRT_MAX

BLKSECTGET ioctl loads the request queue's max_sectors as unsigned
short value to the argument pointer.  So if the max_sector is greater
than USHRT_MAX, the upper 16 bits of that is just discarded.

In such case, USHRT_MAX is more preferable than the lower 16 bits of
max_sectors.

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>

1 files changed, 4 insertions, 1 deletions

diff --git a/block/ioctl.c b/block/ioctl.c
index 7d5c3b20af45..d6cda8147c91 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -278,6 +278,7 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
         struct backing_dev_info *bdi;
         loff_t size;
         int ret, n;
+        unsigned int max_sectors;
 
         switch(cmd) {
         case BLKFLSBUF:
@@ -375,7 +376,9 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
         case BLKDISCARDZEROES:
                 return put_uint(arg, bdev_discard_zeroes_data(bdev));
         case BLKSECTGET:
-                return put_ushort(arg, queue_max_sectors(bdev_get_queue(bdev)));
+                max_sectors = min_t(unsigned int, USHRT_MAX,
+                                    queue_max_sectors(bdev_get_queue(bdev)));
+                return put_ushort(arg, max_sectors);
         case BLKROTATIONAL:
                 return put_ushort(arg, !blk_queue_nonrot(bdev_get_queue(bdev)));
         case BLKRASET: