Re: [PATCH v5] btrfs: Don't submit any btree write bio if the fs has error

[David Sterba <dsterba@suse.cz>]

On Wed, Feb 12, 2020 at 02:12:44PM +0800, Qu Wenruo wrote:
> @@ -4036,7 +4037,39 @@ int btree_write_cache_pages(struct address_space *mapping,
>  		end_write_bio(&epd, ret);
>  		return ret;
>  	}
> -	ret = flush_write_bio(&epd);
> +	/*
> +	 * If something went wrong, don't allow any metadata write bio to be
> +	 * submitted.
> +	 *
> +	 * This would prevent use-after-free if we had dirty pages not
> +	 * cleaned up, which can still happen by fuzzed images.
> +	 *
> +	 * - Bad extent tree
> +	 *   Allowing existing tree block to be allocated for other trees.
> +	 *
> +	 * - Log tree operations
> +	 *   Exiting tree blocks get allocated to log tree, bumps its
> +	 *   generation, then get cleaned in tree re-balance.
> +	 *   Such tree block will not be written back, since it's clean,
> +	 *   thus no WRITTEN flag set.
> +	 *   And after log writes back, this tree block is not traced by
> +	 *   any dirty extent_io_tree.
> +	 *
> +	 * - Offending tree block gets re-dirtied from its original owner
> +	 *   Since it has bumped generation, no WRITTEN flag, it can be
> +	 *   reused without COWing. This tree block will not be traced
> +	 *   by btrfs_transaction::dirty_pages.
> +	 *
> +	 *   Now such dirty tree block will not be cleaned by any dirty
> +	 *   extent io tree. Thus we don't want to submit such wild eb
> +	 *   if the fs already has error.
> +	 */
> +	if (!test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) {
> +		ret = flush_write_bio(&epd);
> +	} else {
> +		ret = -EUCLEAN;
> +		end_write_bio(&epd, ret);
> +	}

This replaces one instance of flush_write_bio, would it make sense to
wrap it to flush_write_bio or some other helper? There might be places
where not handling the fs error state would be acceptable, so eg.

flush_write_bio = as it is now

flush_write_bio_or_end = does the above