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-prev] [day] [month] [year] [list]
Message-Id: <1371843030-24038-2-git-send-email-tytso@mit.edu>
Date:	Fri, 21 Jun 2013 15:30:30 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	desrt@...rt.ca, Theodore Ts'o <tytso@....edu>
Subject: [PATCH 2/2] ext4: allocate delayed allocation blocks before rename

When ext4_rename() overwrites an already existing file, call
ext4_alloc_da_blocks() before starting the journal handle which
actually does the rename, instead of doing this afterwards.  This
improves the likelihood that the contents will survive a crash if an
application replaces a file using the sequence:

1)  write replacement contents to foo.new
2)  <omit fsync of foo.new>
3)  rename foo.new to foo

It is still not a guarantee, since ext4_alloc_da_blocks() is *not*
doing a file integrity sync; this means if foo.new is a very large
file, it may not be completely flushed out to disk.

However, for files smaller than a megabyte or so, any dirty pages
should be flushed out before we do the rename operation, and so at the
next journal commit, the CACHE FLUSH command will make sure al of
these pages are safely on the disk platter.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/namei.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index f57980c..ca8174b 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2961,6 +2961,10 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle,
 /*
  * Anybody can rename anything with this: the permission checks are left to the
  * higher-level routines.
+ *
+ * n.b.  old_{dentry,inode) refers to the source dentry/inode
+ * while new_{dentry,inode) refers to the destination dentry/inode
+ * This comes from rename(const char *oldpath, const char *newpath)
  */
 static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 		       struct inode *new_dir, struct dentry *new_dentry)
@@ -2969,7 +2973,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 	struct inode *old_inode, *new_inode;
 	struct buffer_head *old_bh, *new_bh, *dir_bh;
 	struct ext4_dir_entry_2 *old_de, *new_de;
-	int retval, force_da_alloc = 0;
+	int retval;
 	int inlined = 0, new_inlined = 0;
 	struct ext4_dir_entry_2 *parent_de;
 
@@ -3004,6 +3008,8 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 			new_bh = NULL;
 		}
 	}
+	if (new_inode && !test_opt(new_dir->i_sb, NO_AUTO_DA_ALLOC))
+		ext4_alloc_da_blocks(old_inode);
 
 	handle = ext4_journal_start(old_dir, EXT4_HT_DIR,
 		(2 * EXT4_DATA_TRANS_BLOCKS(old_dir->i_sb) +
@@ -3144,8 +3150,6 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 		ext4_mark_inode_dirty(handle, new_inode);
 		if (!new_inode->i_nlink)
 			ext4_orphan_add(handle, new_inode);
-		if (!test_opt(new_dir->i_sb, NO_AUTO_DA_ALLOC))
-			force_da_alloc = 1;
 	}
 	retval = 0;
 
@@ -3155,8 +3159,6 @@ end_rename:
 	brelse(new_bh);
 	if (handle)
 		ext4_journal_stop(handle);
-	if (retval == 0 && force_da_alloc)
-		ext4_alloc_da_blocks(old_inode);
 	return retval;
 }
 
-- 
1.7.12.rc0.22.gcdd159b

--
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

Powered by blists - more mailing lists