From 2ba48b20049b5a76f34a85f853c9496d1b10533a Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 22 Dec 2022 07:59:17 +0800 Subject: btrfs: fix compat_ro checks against remount [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 Fixes: 81d5d61454c3 ("btrfs: enhance unsupported compat RO flags handling") CC: stable@vger.kernel.org # 5.15+ Reviewed-by: Anand Jain Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/disk-io.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'fs/btrfs/disk-io.c') diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 9940cc39dbc9..8aeaada1fcae 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -3384,6 +3384,8 @@ 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). * @@ -3394,7 +3396,7 @@ 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); @@ -3433,7 +3435,7 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, struct super_block *sb) 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); @@ -3636,7 +3638,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device 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; -- cgit v1.2.3