[PATCH 4.4-cip 11/23] btrfs: fix int32 overflow in shrink_delalloc().

Ben Hutchings <ben.hutchings@...>

From: Adam Borowski <kilobyte@...>

commit 8eb0dfdbda3f56bf7d248ed87fcc383df114ecbb upstream.

UBSAN: Undefined behaviour in fs/btrfs/extent-tree.c:4623:21
signed integer overflow:
10808 * 262144 cannot be represented in type 'int [8]'

If 8192<=items<16384, we request a writeback of an insane number of pages
which is benign (everything will be written). But if items>=16384, the
space reservation won't be enough.

Signed-off-by: Adam Borowski <kilobyte@...>
Reviewed-by: David Sterba <dsterba@...>
Signed-off-by: David Sterba <dsterba@...>
Signed-off-by: Ben Hutchings <ben.hutchings@...>
fs/btrfs/extent-tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 47cdc6f3390b..a4d7dbe2619e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4568,7 +4568,7 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,

/* Calc the number of the pages we need flush for space reservation */
items = calc_reclaim_items_nr(root, to_reclaim);
- to_reclaim = items * EXTENT_SIZE_PER_ITEM;
+ to_reclaim = (u64)items * EXTENT_SIZE_PER_ITEM;

trans = (struct btrfs_trans_handle *)current->journal_info;
block_rsv = &root->fs_info->delalloc_block_rsv;

Ben Hutchings
Software Developer, Codethink Ltd.

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