linux-ext4 - [PATCH 03/32] libext2fs: fix 64bit overflow in ext2fs_block_alloc_stats

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Date:	Sat, 01 Mar 2014 23:16:58 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	tytso@....edu, darrick.wong@...cle.com
Cc:	linux-ext4@...r.kernel.org
Subject: [PATCH 03/32] libext2fs: fix 64bit overflow in
 ext2fs_block_alloc_stats_range

In ext2fs_block_alloc_stats_range(), the quantity "-inuse * n" is
calculated as a signed 32-bit quantity.  Unfortunately, gcc (4.6.3 on
Ubuntu 12.04) doesn't sign-extend this quantity to fill the blk64_t
parameter that ext2fs_free_blocks_count_add() wants, so the end result
is that the superblock gets a ridiculously huge free block count.

Changing the declaration of 'n' to blk64_t seems to fix this.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 lib/ext2fs/alloc_stats.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/ext2fs/alloc_stats.c b/lib/ext2fs/alloc_stats.c
index 5bb86ef..4feb24d 100644
--- a/lib/ext2fs/alloc_stats.c
+++ b/lib/ext2fs/alloc_stats.c
@@ -129,7 +129,7 @@ void ext2fs_block_alloc_stats_range(ext2_filsys fs, blk64_t blk,
 	while (num) {
 		int group = ext2fs_group_of_blk2(fs, blk);
 		blk64_t last_blk = ext2fs_group_last_block2(fs, group);
-		blk_t n = num;
+		blk64_t n = num;

 		if (blk + num > last_blk)
 			n = last_blk - blk + 1;

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