The patch below does not apply to the 4.19-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@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 829b37b8cddb1db75c1b7905505b90e593b15db1 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@xxxxxxx>
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@xxxxxxxxxx
Reported-by: syzbot+bca9799bf129256190da@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
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");
