This is a note to let you know that I've just added the patch titled
btrfs: fix compat_ro checks against remount
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-compat_ro-checks-against-remount.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2ba48b20049b5a76f34a85f853c9496d1b10533a Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@xxxxxxxx>
Date: Thu, 22 Dec 2022 07:59:17 +0800
Subject: btrfs: fix compat_ro checks against remount
From: Qu Wenruo <wqu@xxxxxxxx>
commit 2ba48b20049b5a76f34a85f853c9496d1b10533a upstream.
[BUG]
Even with commit 81d5d61454c3 ("btrfs: enhance unsupported compat RO
flags handling"), btrfs can still mount a fs with unsupported compat_ro
flags read-only, then remount it RW:
# btrfs ins dump-super /dev/loop0 | grep compat_ro_flags -A 3
compat_ro_flags 0x403
( FREE_SPACE_TREE |
FREE_SPACE_TREE_VALID |
unknown flag: 0x400 )
# mount /dev/loop0 /mnt/btrfs
mount: /mnt/btrfs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
dmesg(1) may have more information after failed mount system call.
^^^ RW mount failed as expected ^^^
# dmesg -t | tail -n5
loop0: detected capacity change from 0 to 1048576
BTRFS: device fsid cb5b82f5-0fdd-4d81-9b4b-78533c324afa devid 1 transid 7 /dev/loop0 scanned by mount (1146)
BTRFS info (device loop0): using crc32c (crc32c-intel) checksum algorithm
BTRFS info (device loop0): using free space tree
BTRFS error (device loop0): cannot mount read-write because of unknown compat_ro features (0x403)
BTRFS error (device loop0): open_ctree failed
# mount /dev/loop0 -o ro /mnt/btrfs
# mount -o remount,rw /mnt/btrfs
^^^ RW remount succeeded unexpectedly ^^^
[CAUSE]
Currently we use btrfs_check_features() to check compat_ro flags against
our current mount flags.
That function get reused between open_ctree() and btrfs_remount().
But for btrfs_remount(), the super block we passed in still has the old
mount flags, thus btrfs_check_features() still believes we're mounting
read-only.
[FIX]
Replace the existing @sb argument with @is_rw_mount.
As originally we only use @sb to determine if the mount is RW.
Now it's callers' responsibility to determine if the mount is RW, and
since there are only two callers, the check is pretty simple:
- caller in open_ctree()
Just pass !sb_rdonly().
- caller in btrfs_remount()
Pass !(*flags & SB_RDONLY), as our check should be against the new
flags.
Now we can correctly reject the RW remount:
# mount /dev/loop0 -o ro /mnt/btrfs
# mount -o remount,rw /mnt/btrfs
mount: /mnt/btrfs: mount point not mounted or bad option.
dmesg(1) may have more information after failed mount system call.
# dmesg -t | tail -n 1
BTRFS error (device loop0: state M): cannot mount read-write because of unknown compat_ro features (0x403)
Reported-by: Chung-Chiang Cheng <shepjeng@xxxxxxxxx>
Fixes: 81d5d61454c3 ("btrfs: enhance unsupported compat RO flags handling")
CC: stable@xxxxxxxxxxxxxxx # 5.15+
Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/disk-io.c | 8 +++++---
fs/btrfs/disk-io.h | 2 +-
fs/btrfs/super.c | 2 +-
3 files changed, 7 insertions(+), 5 deletions(-)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3296,6 +3296,8 @@ out:
/*
* Do various sanity and dependency checks of different features.
*
+ * @is_rw_mount: If the mount is read-write.
+ *
* This is the place for less strict checks (like for subpage or artificial
* feature dependencies).
*
@@ -3306,7 +3308,7 @@ out:
* (space cache related) can modify on-disk format like free space tree and
* screw up certain feature dependencies.
*/
-int btrfs_check_features(struct btrfs_fs_info *fs_info, struct super_block *sb)
+int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
{
struct btrfs_super_block *disk_super = fs_info->super_copy;
u64 incompat = btrfs_super_incompat_flags(disk_super);
@@ -3345,7 +3347,7 @@ int btrfs_check_features(struct btrfs_fs
if (btrfs_super_nodesize(disk_super) > PAGE_SIZE)
incompat |= BTRFS_FEATURE_INCOMPAT_BIG_METADATA;
- if (compat_ro_unsupp && !sb_rdonly(sb)) {
+ if (compat_ro_unsupp && is_rw_mount) {
btrfs_err(fs_info,
"cannot mount read-write because of unknown compat_ro features (0x%llx)",
compat_ro);
@@ -3548,7 +3550,7 @@ int __cold open_ctree(struct super_block
goto fail_alloc;
}
- ret = btrfs_check_features(fs_info, sb);
+ ret = btrfs_check_features(fs_info, !sb_rdonly(sb));
if (ret < 0) {
err = ret;
goto fail_alloc;
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -50,7 +50,7 @@ int __cold open_ctree(struct super_block
void __cold close_ctree(struct btrfs_fs_info *fs_info);
int btrfs_validate_super(struct btrfs_fs_info *fs_info,
struct btrfs_super_block *sb, int mirror_num);
-int btrfs_check_features(struct btrfs_fs_info *fs_info, struct super_block *sb);
+int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount);
int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors);
struct btrfs_super_block *btrfs_read_dev_super(struct block_device *bdev);
struct btrfs_super_block *btrfs_read_dev_one_super(struct block_device *bdev,
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2014,7 +2014,7 @@ static int btrfs_remount(struct super_bl
if (ret)
goto restore;
- ret = btrfs_check_features(fs_info, sb);
+ ret = btrfs_check_features(fs_info, !(*flags & SB_RDONLY));
if (ret < 0)
goto restore;
Patches currently in stable-queue which might be from wqu@xxxxxxxx are
queue-6.1/btrfs-fix-compat_ro-checks-against-remount.patch
