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

[Anand Jain <anand.jain@oracle.com>]

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;
>