This is a note to let you know that I've just added the patch titled

ext4: prevent data corruption with inline data + DAX

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: ext4-prevent-data-corruption-with-inline-data-dax.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 559db4c6d784ceedc2a5418ced4d357cb843e221 Mon Sep 17 00:00:00 2001

From: Ross Zwisler ross.zwisler@linux.intel.com Date: Thu, 12 Oct 2017 11:52:34 -0400 Subject: ext4: prevent data corruption with inline data + DAX

From: Ross Zwisler ross.zwisler@linux.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@linux.intel.com Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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;

Patches currently in stable-queue which might be from ross.zwisler@linux.intel.com are

queue-4.14/ext4-prevent-data-corruption-with-journaling-dax.patch queue-4.14/ext4-prevent-data-corruption-with-inline-data-dax.patch