From: Qu Wenruo wqu@suse.com
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@gmail.com Fixes: 81d5d61454c3 ("btrfs: enhance unsupported compat RO flags handling") CC: stable@vger.kernel.org # 5.15+ Reviewed-by: Anand Jain anand.jain@oracle.com Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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;