[patch] xfs: check for underflow in xfs_iformat_fork()

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

The "di_size" variable comes from the disk and it's a signed 64 bit.
We check the upper limit but we should check for negative numbers as
well.

Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

diff --git a/fs/xfs/xfs_inode_fork.c b/fs/xfs/xfs_inode_fork.c
index 123971b..849fc70 100644
--- a/fs/xfs/xfs_inode_fork.c
+++ b/fs/xfs/xfs_inode_fork.c
@@ -167,7 +167,8 @@ xfs_iformat_fork(
                        }
 
                        di_size = be64_to_cpu(dip->di_size);
-                       if (unlikely(di_size > XFS_DFORK_DSIZE(dip, 
ip->i_mount))) {
+                       if (unlikely(di_size < 0 ||
+                                    di_size > XFS_DFORK_DSIZE(dip, 
ip->i_mount))) {
                                xfs_warn(ip->i_mount,
                        "corrupt inode %Lu (bad size %Ld for local inode).",
                                        (unsigned long long) ip->i_ino,