[PATCH AUTOSEL for 4.9 061/156] afs: Fix the maths in afs_fs_store_data()

[alexander . levin]

From: David Howells <dhowells@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
---
 fs/afs/fsclient.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index fed95c34bdc0..2ae86018fcb7 100644
--- 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;
-- 
2.11.0