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    Subject[PATCH 5.4 276/389] btrfs: reject log replay if there is unsupported RO compat flag
    Date
    From: Qu Wenruo <wqu@suse.com>

    commit dc4d31684974d140250f3ee612c3f0cab13b3146 upstream.

    [BUG]
    If we have a btrfs image with dirty log, along with an unsupported RO
    compatible flag:

    log_root 30474240
    ...
    compat_flags 0x0
    compat_ro_flags 0x40000003
    ( FREE_SPACE_TREE |
    FREE_SPACE_TREE_VALID |
    unknown flag: 0x40000000 )

    Then even if we can only mount it RO, we will still cause metadata
    update for log replay:

    BTRFS info (device dm-1): flagging fs with big metadata feature
    BTRFS info (device dm-1): using free space tree
    BTRFS info (device dm-1): has skinny extents
    BTRFS info (device dm-1): start tree-log replay

    This is definitely against RO compact flag requirement.

    [CAUSE]
    RO compact flag only forces us to do RO mount, but we will still do log
    replay for plain RO mount.

    Thus this will result us to do log replay and update metadata.

    This can be very problematic for new RO compat flag, for example older
    kernel can not understand v2 cache, and if we allow metadata update on
    RO mount and invalidate/corrupt v2 cache.

    [FIX]
    Just reject the mount unless rescue=nologreplay is provided:

    BTRFS error (device dm-1): cannot replay dirty log with unsupport optional features (0x40000000), try rescue=nologreplay instead

    We don't want to set rescue=nologreply directly, as this would make the
    end user to read the old data, and cause confusion.

    Since the such case is really rare, we're mostly fine to just reject the
    mount with an error message, which also includes the proper workaround.

    CC: stable@vger.kernel.org #4.9+
    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 | 14 ++++++++++++++
    1 file changed, 14 insertions(+)

    --- a/fs/btrfs/disk-io.c
    +++ b/fs/btrfs/disk-io.c
    @@ -2970,6 +2970,20 @@ int open_ctree(struct super_block *sb,
    err = -EINVAL;
    goto fail_csum;
    }
    + /*
    + * We have unsupported RO compat features, although RO mounted, we
    + * should not cause any metadata write, including log replay.
    + * Or we could screw up whatever the new feature requires.
    + */
    + if (unlikely(features && btrfs_super_log_root(disk_super) &&
    + !btrfs_test_opt(fs_info, NOLOGREPLAY))) {
    + btrfs_err(fs_info,
    +"cannot replay dirty log with unsupported compat_ro features (0x%llx), try rescue=nologreplay",
    + features);
    + err = -EINVAL;
    + goto fail_alloc;
    + }
    +

    ret = btrfs_init_workqueues(fs_info, fs_devices);
    if (ret) {

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