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

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Date:   Thu,  2 Feb 2023 20:44:27 +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 5/5] btrfs: 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/btrfs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 98a800b8bd43..b61ec4bb9cf0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5234,6 +5234,7 @@ static int btrfs_setsize(struct inode *inode, struct iattr *attr)
 		i_size_write(inode, newsize);
 		btrfs_inode_safe_disk_i_size_write(BTRFS_I(inode), 0);
 		pagecache_isize_extended(inode, oldsize, newsize);
+		truncate_pagecache(inode, oldsize);
 		ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
 		btrfs_drew_write_unlock(&root->snapshot_lock);
 		btrfs_end_transaction(trans);
-- 
2.35.1