linux-ext4 - [PATCH 2/5] ext4: Zero bytes after 'oldsize' if we're expanding the file

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Date:   Thu,  2 Feb 2023 20:44:24 +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 2/5] ext4: 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/ext4/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9d9f414f99fe..14e3fa99f733 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5604,6 +5604,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 			if (!shrink) {
 				pagecache_isize_extended(inode, oldsize,
 							 inode->i_size);
+				truncate_pagecache(inode, oldsize);
 			} else if (ext4_should_journal_data(inode)) {
 				ext4_wait_for_tail_page_commit(inode);
 			}
-- 
2.35.1