linux-kernel - [PATCH] ext4: avoid exposure of stale data in ext4_punch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130927155329.3272.64086.stgit@dhcp-10-30-17-2.sw.ru>
Date:	Fri, 27 Sep 2013 19:54:03 +0400
From:	Maxim Patlasov <MPatlasov@...allels.com>
To:	tytso@....edu
Cc:	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, jack@...e.cz,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ext4: avoid exposure of stale data in ext4_punch_hole() -v2

While handling punch-hole fallocate, it's useless to truncate page cache
before removing the range from extent tree (or block map in indirect case)
because page cache can be re-populated (by read-ahead or read(2) or mmap-ed
read) immediately after truncating page cache, but before updating extent
tree (or block map). In that case the user will see stale data even after
fallocate is completed.

Changed in v2 (Thanks to Jan Kara):
 - Until the problem of data corruption resulting from pages backed by
   already freed blocks is fully resolved, the simple thing we can do now
   is to add another truncation of pagecache after punch hole is done.

Signed-off-by: Maxim Patlasov <mpatlasov@...allels.com>
---
 fs/ext4/inode.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0d424d7..2984ddf 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3621,6 +3621,12 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
 	up_write(&EXT4_I(inode)->i_data_sem);
 	if (IS_SYNC(inode))
 		ext4_handle_sync(handle);
+
+	/* Now release the pages again to reduce race window */
+	if (last_block_offset > first_block_offset)
+		truncate_pagecache_range(inode, first_block_offset,
+					 last_block_offset);
+
 	inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
 	ext4_mark_inode_dirty(handle, inode);
 out_stop:

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/