linux-kernel - [PATCH 4/5] afs: Zero bytes after 'oldsize' if we're expanding the file

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Date:   Thu,  2 Feb 2023 20:44:26 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-afs@...ts.infradead.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-mm@...ck.org,
        Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
        fstests@...r.kernel.org
Subject: [PATCH 4/5] afs: Zero bytes after 'oldsize' if we're expanding the file

POSIX requires that "If the file size is increased, the extended area
shall appear as if it were zero-filled".  It is possible to use mmap to
write past EOF and that data will become visible instead of zeroes.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 fs/afs/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 6d3a3dbe4928..92e2ba7625de 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -854,6 +854,8 @@ static void afs_setattr_edit_file(struct afs_operation *op)
 
 		if (size < i_size)
 			truncate_pagecache(inode, size);
+		else
+			truncate_pagecache(inode, i_size);
 		if (size != i_size)
 			fscache_resize_cookie(afs_vnode_cache(vp->vnode),
 					      vp->scb.status.size);
-- 
2.35.1