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Commit 5dbb6255 authored by Theodore Ts'o's avatar Theodore Ts'o Committed by Greg Kroah-Hartman
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ext4: avoid race conditions when remounting with options that change dax 



[ Upstream commit 829b37b8cddb1db75c1b7905505b90e593b15db1 ]

Trying to change dax mount options when remounting could allow mount
options to be enabled for a small amount of time, and then the mount
option change would be reverted.

In the case of "mount -o remount,dax", this can cause a race where
files would temporarily treated as DAX --- and then not.

Cc: stable@kernel.org
Reported-by: default avatar <syzbot+bca9799bf129256190da@syzkaller.appspotmail.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 051bf267

fs/ext4/super.c

+10 −12
Original line number Diff line number Diff line
@@ -1989,6 +1989,16 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token, 
#endif

	} else if (token == Opt_dax) {

#ifdef CONFIG_FS_DAX

		if (is_remount && test_opt(sb, DAX)) {

			ext4_msg(sb, KERN_ERR, "can't mount with "

				"both data=journal and dax");

			return -1;

		}

		if (is_remount && !(sbi->s_mount_opt & EXT4_MOUNT_DAX)) {

			ext4_msg(sb, KERN_ERR, "can't change "

					"dax mount option while remounting");

			return -1;

		}

		ext4_msg(sb, KERN_WARNING,

		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");

			sbi->s_mount_opt |= m->mount_opt;
@@ -5274,12 +5284,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
			err = -EINVAL;

			goto restore_opts;

		}

		if (test_opt(sb, DAX)) {

			ext4_msg(sb, KERN_ERR, "can't mount with "

				 "both data=journal and dax");

			err = -EINVAL;

			goto restore_opts;

		}

	} else if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_ORDERED_DATA) {

		if (test_opt(sb, JOURNAL_ASYNC_COMMIT)) {

			ext4_msg(sb, KERN_ERR, "can't mount with "
@@ -5295,12 +5299,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) 
		goto restore_opts;

	}



	if ((sbi->s_mount_opt ^ old_opts.s_mount_opt) & EXT4_MOUNT_DAX) {

		ext4_msg(sb, KERN_WARNING, "warning: refusing change of "

			"dax flag with busy inodes while remounting");

		sbi->s_mount_opt ^= EXT4_MOUNT_DAX;

	}



	if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)

		ext4_abort(sb, "Abort forced by user");