linux-kernel - [PATCH 4.9 084/177] afs: Fix the maths in afs_fs_store

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Date:   Mon, 18 Dec 2017 16:48:27 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.9 084/177] afs: Fix the maths in afs_fs_store_data()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@...hat.com>


[ 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@...hat.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/afs/fsclient.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -1178,7 +1178,7 @@ int afs_fs_store_data(struct afs_server
 	_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;