[PATCH 2/4] fs: btrfs: volumes: prevent overflow for multiplying

[Qu Wenruo <wqu@suse.com>]

In __btrfs_map_block() we do a int * int and assign it to u64.
This is not safe as the result (int * int) is still evaluated as (int)
thus it can overflow.

Convert one of the multiplier to u64 to prevent such problem.

In real world, this should not cause problem as we have device number
limit thus it won't go beyond 4G for a single stripe.

But it's harder to teach coverity about all these hidden limits, so just
fix the possible overflow.

Reported-by: Coverity CID 312957
Reported-by: Coverity CID 312948
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/volumes.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index fcf52d4b0ff3..4aaaeab663f5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1030,7 +1030,7 @@ again:
 	 */
 	stripe_nr = stripe_nr / map->stripe_len;
 
-	stripe_offset = stripe_nr * map->stripe_len;
+	stripe_offset = stripe_nr * (u64)map->stripe_len;
 	BUG_ON(offset < stripe_offset);
 
 	/* stripe_offset is the offset of this block in its stripe*/
@@ -1103,7 +1103,7 @@ again:
 			rot = stripe_nr % map->num_stripes;
 
 			/* Fill in the logical address of each stripe */
-			tmp = stripe_nr * nr_data_stripes(map);
+			tmp = (u64)stripe_nr * nr_data_stripes(map);
 
 			for (i = 0; i < nr_data_stripes(map); i++)
 				raid_map[(i+rot) % map->num_stripes] =
-- 
2.29.1