linux-kernel - [PATCH 4.14 085/193] ext4: prevent data corruption with inline data + DAX

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Date:   Tue, 28 Nov 2017 11:25:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Theodore Tso <tytso@....edu>, Jan Kara <jack@...e.cz>
Subject: [PATCH 4.14 085/193] ext4: prevent data corruption with inline data + DAX

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ross Zwisler <ross.zwisler@...ux.intel.com>

commit 559db4c6d784ceedc2a5418ced4d357cb843e221 upstream.

If an inode has inline data it is currently prevented from using DAX by a
check in ext4_set_inode_flags().  When the inode grows inline data via
ext4_create_inline_data() or removes its inline data via
ext4_destroy_inline_data_nolock(), the value of S_DAX can change.

Currently these changes are unsafe because we don't hold off page faults
and I/O, write back dirty radix tree entries and invalidate all mappings.
There are also issues with mm-level races when changing the value of S_DAX,
as well as issues with the VM_MIXEDMAP flag:

https://www.spinics.net/lists/linux-xfs/msg09859.html

The unsafe transition of S_DAX can reliably cause data corruption, as shown
by the following fstest:

https://patchwork.kernel.org/patch/9948381/

Fix this issue by preventing the DAX mount option from being used on
filesystems that were created to support inline data.  Inline data is an
option given to mkfs.ext4.

Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/inline.c |   10 ----------
 fs/ext4/super.c  |    5 +++++
 2 files changed, 5 insertions(+), 10 deletions(-)

--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -302,11 +302,6 @@ static int ext4_create_inline_data(handl
 	EXT4_I(inode)->i_inline_size = len + EXT4_MIN_INLINE_DATA_SIZE;
 	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
 	ext4_set_inode_flag(inode, EXT4_INODE_INLINE_DATA);
-	/*
-	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
-	 * get cleared
-	 */
-	ext4_set_inode_flags(inode);
 	get_bh(is.iloc.bh);
 	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
 
@@ -451,11 +446,6 @@ static int ext4_destroy_inline_data_nolo
 		}
 	}
 	ext4_clear_inode_flag(inode, EXT4_INODE_INLINE_DATA);
-	/*
-	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
-	 * get set.
-	 */
-	ext4_set_inode_flags(inode);
 
 	get_bh(is.iloc.bh);
 	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3708,6 +3708,11 @@ static int ext4_fill_super(struct super_
 	}
 
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
+		if (ext4_has_feature_inline_data(sb)) {
+			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
+					" that may contain inline data");
+			goto failed_mount;
+		}
 		err = bdev_dax_supported(sb, blocksize);
 		if (err)
 			goto failed_mount;