[PATCH 4.5 112/128] btrfs: avoid overflowing f_bfree

Greg Kroah-Hartman
2016-06-06T14:39:46Z

From: Luis de Bethencourt <luisbg@osg.samsung.com>

commit 41b34accb265e3a20211a7a8ef3625678f1c6ec7 upstream.

Since mixed block groups accounting isn't byte-accurate and f_bree is an
unsigned integer, it could overflow. Avoid this.

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Suggested-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/super.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2073,7 +2073,11 @@ static int btrfs_statfs(struct dentry *d

/* Account global block reserve as used, it's in logical size already */
spin_lock(&block_rsv->lock);
- buf->f_bfree -= block_rsv->size >> bits;
+ /* Mixed block groups accounting is not byte-accurate, avoid overflow */
+ if (buf->f_bfree >= block_rsv->size >> bits)
+ buf->f_bfree -= block_rsv->size >> bits;
+ else
+ buf->f_bfree = 0;
spin_unlock(&block_rsv->lock);

buf->f_bavail = div_u64(total_free_data, factor);