The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 829b37b8cddb1db75c1b7905505b90e593b15db1 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o tytso@mit.edu Date: Wed, 10 Jun 2020 11:16:37 -0400 Subject: [PATCH] ext4: avoid race conditions when remounting with options that change dax
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: syzbot+bca9799bf129256190da@syzkaller.appspotmail.com Signed-off-by: Theodore Ts'o tytso@mit.edu
diff --git a/fs/ext4/super.c b/fs/ext4/super.c index a22d67c5bc00..edf06c1bee9d 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -2104,16 +2104,40 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token, switch (token) { case Opt_dax: case Opt_dax_always: + if (is_remount && + (!(sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) || + (sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER))) { + fail_dax_change_remount: + ext4_msg(sb, KERN_ERR, "can't change " + "dax mount option while remounting"); + return -1; + } + if (is_remount && + (test_opt(sb, DATA_FLAGS) == + EXT4_MOUNT_JOURNAL_DATA)) { + ext4_msg(sb, KERN_ERR, "can't mount with " + "both data=journal and dax"); + return -1; + } ext4_msg(sb, KERN_WARNING, "DAX enabled. Warning: EXPERIMENTAL, use at your own risk"); sbi->s_mount_opt |= EXT4_MOUNT_DAX_ALWAYS; sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER; break; case Opt_dax_never: + if (is_remount && + (!(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER) || + (sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS))) + goto fail_dax_change_remount; sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER; sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS; break; case Opt_dax_inode: + if (is_remount && + ((sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) || + (sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER) || + !(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_INODE))) + goto fail_dax_change_remount; sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS; sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER; /* Strictly for printing options */ @@ -5454,12 +5478,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) err = -EINVAL; goto restore_opts; } - if (test_opt(sb, DAX_ALWAYS)) { - 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 " @@ -5475,18 +5493,6 @@ 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_ALWAYS || - (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2) & EXT4_MOUNT2_DAX_NEVER || - (sbi->s_mount_opt2 ^ old_opts.s_mount_opt2) & EXT4_MOUNT2_DAX_INODE) { - ext4_msg(sb, KERN_WARNING, "warning: refusing change of " - "dax mount option with busy inodes while remounting"); - sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS; - sbi->s_mount_opt |= old_opts.s_mount_opt & EXT4_MOUNT_DAX_ALWAYS; - sbi->s_mount_opt2 &= ~(EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE); - sbi->s_mount_opt2 |= old_opts.s_mount_opt2 & - (EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE); - } - if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED) ext4_abort(sb, EXT4_ERR_ESHUTDOWN, "Abort forced by user");