afs: Fix the maths in afs_fs_store_data()

afs_fs_store_data() works out of the size of the write it's going to make,
but it uses 32-bit unsigned subtraction in one place that gets
automatically cast to loff_t.

However, if to < offset, then the number goes negative, but as the result
isn't signed, this doesn't get sign-extended to 64-bits when placed in a
loff_t.

Fix by casting the operands to loff_t.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index 0778c5b6b59b..d9234b767287 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -1236,7 +1236,7 @@ int afs_fs_store_data(struct afs_server *server, struct afs_writeback *wb,
         _enter(",%x,{%x:%u},,",
                key_serial(wb->key), vnode->fid.vid, vnode->fid.vnode);
 
-        size = to - offset;
+        size = (loff_t)to - (loff_t)offset;
         if (first != last)
                 size += (loff_t)(last - first) << PAGE_SHIFT;
         pos = (loff_t)first << PAGE_SHIFT;