From: Theodore Ts'o <tytso@xxxxxxx>
[ 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@xxxxxxxxxx
Reported-by: syzbot+bca9799bf129256190da@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/ext4/super.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 830160ad07a63..f7c20bb20da37 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2034,6 +2034,16 @@ 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;
@@ -5367,12 +5377,6 @@ 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 "
@@ -5388,12 +5392,6 @@ 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");
--
2.25.1
