btrfs: avoid overflow when sector_t is 32 bit

Jean-Denis Girard noticed commit c821e7f "pass bytes to
btrfs_bio_alloc" (https://patchwork.kernel.org/patch/9763081/)
introduces a regression on 32 bit machines.
When CONFIG_LBDAF is _not_ defined (CONFIG_LBDAF == Support for large
(2TB+) block devices and files) sector_t is 32 bit on 32bit machines.

In the function submit_extent_page, 'sector' (which is sector_t type) is
multiplied by 512 to convert it from sectors to bytes, leading to an
overflow when the disk is bigger than 4GB (!).

I added a cast to u64 to avoid overflow.

Fixes: c821e7f ("btrfs: pass bytes to btrfs_bio_alloc")
CC: [email protected] # 4.13+
Signed-off-by: Goffredo Baroncelli <[email protected]>
Tested-by: Jean-Denis Girard <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

fs/btrfs/extent_io.c

@@ -2801,7 +2801,7 @@ static int submit_extent_page(unsigned int opf, struct extent_io_tree *tree,
 		}
 	}
 
-	bio = btrfs_bio_alloc(bdev, sector << 9);
+	bio = btrfs_bio_alloc(bdev, (u64)sector << 9);
 	bio_add_page(bio, page, page_size, offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;