afs: Fix the maths in afs_fs_store_data()

[ Upstream commit 146a1192783697810b63a1e41c4d59fc93387340 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index fed95c3..2ae8601 100644 (file)
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -1178,7 +1178,7 @@ 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;