[PATCH v3] erofs-utils: lib: Fix 8MB bug on uncompressed extent size

[Gao Xiang]

On Tue, Feb 08, 2022 at 10:43:17AM -0800, Kelvin Zhang wrote:
> Previously, uncompressed extent can be at most 8MB before mkfs.erofs
> crashes on some error condition. This is due to a minor bug in how
> compressed indices are encoded. This patch fixes the issue.
> 
> Signed-off-by: Kelvin Zhang <zhangkelvin at google.com>
> ---
>  lib/compress.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/compress.c b/lib/compress.c
> index 98be7a2..add95f5 100644
> --- a/lib/compress.c
> +++ b/lib/compress.c
> @@ -97,7 +97,23 @@ static void vle_write_indexes(struct z_erofs_vle_compress_ctx *ctx,
>  		} else if (d0) {
>  			type = Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD;
>  
> -			di.di_u.delta[0] = cpu_to_le16(d0);
> +			/*
> +			 * If the |Z_EROFS_VLE_DI_D0_CBLKCNT| bit is set, parser
> +			 * will interpret |delta[0]| as size of pcluster, rather
> +			 * than distance to last head cluster. Normally this
> +			 * isn't a problem, because uncompressed extent size are
> +			 * below Z_EROFS_VLE_DI_D0_CBLKCNT * BLOCK_SIZE = 8MB.
> +			 * But with large pcluster it's possible to go over this
> +			 * number, resulting in corrupted compressed indices.
> +			 * To solve this, we replace d0 with
> +			 * Z_EROFS_VLE_DI_D0_CBLKCNT-1.
> +			 */
> +			if (d0 > Z_EROFS_VLE_DI_D0_CBLKCNT) {

Thanks for the new version.

I think this part would be "if (d0 >= Z_EROFS_VLE_DI_D0_CBLKCNT)",
and already applied with minor styling changes:

https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/commit/?id=789ac9b03c2c0d27c5be81cb8d026e2300ae822e

Thanks,
Gao Xiang

> +				di.di_u.delta[0] = cpu_to_le16(
> +					Z_EROFS_VLE_DI_D0_CBLKCNT-1);
> +			} else {
> +				di.di_u.delta[0] = cpu_to_le16(d0);
> +			}
>  			di.di_u.delta[1] = cpu_to_le16(d1);
>  		} else {
>  			type = raw ? Z_EROFS_VLE_CLUSTER_TYPE_PLAIN :
> -- 
> 2.35.0.263.gb82422642f-goog