linux-ext4 - [PATCH] ext4: Fix deadlock in ext4_write_begin() and ext4_da_write

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-Id: <1235053488-16937-1-git-send-email-jack@suse.cz>
Date:	Thu, 19 Feb 2009 15:24:48 +0100
From:	Jan Kara <jack@...e.cz>
To:	linux-ext4@...r.kernel.org
Cc:	tytso@....edu, Jan Kara <jack@...e.cz>
Subject: [PATCH] ext4: Fix deadlock in ext4_write_begin() and ext4_da_write_begin()

Functions ext4_write_begin() and ext4_da_write_begin() call
grab_cache_page_write_begin() without AOP_FLAG_NOFS. Thus it
can happen that page reclaim is triggered in that function
and it recurses back into the filesystem (or some other filesystem).
But this can lead to various problems as a transaction is already
started at that point. Add the necessary flag.

(Reported in http://bugzilla.kernel.org/show_bug.cgi?id=11688)

Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/inode.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 03ba20b..e62e6e4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1366,6 +1366,10 @@ retry:
 		goto out;
 	}
 
+	/* We cannot recurse into the filesystem as the transaction is already
+	 * started */
+	flags |= AOP_FLAG_NOFS;
+
 	page = grab_cache_page_write_begin(mapping, index, flags);
 	if (!page) {
 		ext4_journal_stop(handle);
@@ -1375,7 +1379,7 @@ retry:
 	*pagep = page;
 
 	ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
-							ext4_get_block);
+				ext4_get_block);
 
 	if (!ret && ext4_should_journal_data(inode)) {
 		ret = walk_page_buffers(handle, page_buffers(page),
@@ -2648,6 +2652,9 @@ retry:
 		ret = PTR_ERR(handle);
 		goto out;
 	}
+	/* We cannot recurse into the filesystem as the transaction is already
+	 * started */
+	flags |= AOP_FLAG_NOFS;
 
 	page = grab_cache_page_write_begin(mapping, index, flags);
 	if (!page) {
-- 
1.6.0.2

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html