Re: [PATCH] btrfs: Do super block verification before writing it to disk

Anand Jain
2018-04-16T12:53:24Z

On 04/16/2018 10:02 AM, Qu Wenruo wrote:
> There are already 2 reports about strangely corrupted super blocks,
> where csum type and incompat flags get some obvious garbage, but csum
> still matches and all other vitals are correct.
>
> This normally means some kernel memory corruption happens, although the
> cause is unknown, at least detect it and prevent further corruption.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---

Can you help point those 2 cases here?

Thanks, Anand

> fs/btrfs/disk-io.c | 24 ++++++++++++++++++++----
> 1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 23803102aa0d..10d814f03f13 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -68,7 +68,8 @@
> static const struct extent_io_ops btree_extent_io_ops;
> static void end_workqueue_fn(struct btrfs_work *work);
> static void free_fs_root(struct btrfs_root *root);
> -static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info);
> +static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> + struct btrfs_super_block *sb);
> static void btrfs_destroy_ordered_extents(struct btrfs_root *root);
> static int btrfs_destroy_delayed_refs(struct btrfs_transaction *trans,
> struct btrfs_fs_info *fs_info);
> @@ -2680,7 +2681,7 @@ int open_ctree(struct super_block *sb,
>
> memcpy(fs_info->fsid, fs_info->super_copy->fsid, BTRFS_FSID_SIZE);
>
> - ret = btrfs_check_super_valid(fs_info);
> + ret = btrfs_check_super_valid(fs_info, fs_info->super_copy);
> if (ret) {
> btrfs_err(fs_info, "superblock contains fatal errors");
> err = -EINVAL;
> @@ -3575,6 +3576,21 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
> sb = fs_info->super_for_commit;
> dev_item = &sb->dev_item;
>
> + /* Do extra check on the sb to be written */
> + ret = btrfs_check_super_valid(fs_info, sb);
> + if (ret) {
> + btrfs_err(fs_info, "fatal superblock corrupted detected");
> + return -EUCLEAN;
> + }
> + /*
> + * Unknown incompat flags can't be mounted, so newly developed flags
> + * means corruption
> + */
> + if (btrfs_super_incompat_flags(sb) & ~BTRFS_FEATURE_INCOMPAT_SUPP) {
> + btrfs_err(fs_info, "fatal superblock corrupted detected");
> + return -EUCLEAN;
> + }
> +
> mutex_lock(&fs_info->fs_devices->device_list_mutex);
> head = &fs_info->fs_devices->devices;
> max_errors = btrfs_super_num_devices(fs_info->super_copy) - 1;
> @@ -3985,9 +4001,9 @@ int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid, int level,
> level, first_key);
> }
>
> -static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info)
> +static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> + struct btrfs_super_block *sb)
> {
> - struct btrfs_super_block *sb = fs_info->super_copy;
> u64 nodesize = btrfs_super_nodesize(sb);
> u64 sectorsize = btrfs_super_sectorsize(sb);
> int ret = 0;
>