[PATCH v2] erofs-utils: lib: fix missing CBLKCNT for big pcluster dedupe

[Yue Hu]

On Wed, 23 Nov 2022 10:30:34 +0800
Gao Xiang <hsiangkao at linux.alibaba.com> wrote:

> CBLKCNT needs to be stored for big pcluster dedupe.  Otherwise,
> the decompression could fail due to incomplete compressed data.
> 
> Reported-by: Yue Hu <huyue2 at coolpad.com>
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Tested-by: Yue Hu <huyue2 at coolpad.com>

> ---
> changes since v1:
>  - fix potential data corruption of v1
> 
>  lib/compress.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/compress.c b/lib/compress.c
> index 17b3213..8f4c63a 100644
> --- a/lib/compress.c
> +++ b/lib/compress.c
> @@ -186,12 +186,22 @@ static int z_erofs_compress_dedupe(struct erofs_inode *inode,
>  		if (z_erofs_dedupe_match(&dctx))
>  			break;
>  
> +		delta = ctx->queue + ctx->head - dctx.cur;
> +		/*
> +		 * For big pcluster dedupe, leave two indices at least to store
> +		 * CBLKCNT as the first step.  Even laterly, an one-block
> +		 * decompresssion could be done as another try in practice.
> +		 */
> +		if (dctx.e.compressedblks > 1 &&
> +		    (ctx->clusterofs + ctx->e.length - delta) % EROFS_BLKSIZ +
> +			dctx.e.length < 2 * EROFS_BLKSIZ)
> +			break;
> +
>  		/* fall back to noncompact indexes for deduplication */
>  		inode->z_advise &= ~Z_EROFS_ADVISE_COMPACTED_2B;
>  		inode->datalayout = EROFS_INODE_FLAT_COMPRESSION_LEGACY;
>  		erofs_sb_set_dedupe();
>  
> -		delta = ctx->queue + ctx->head - dctx.cur;
>  		if (delta) {
>  			DBG_BUGON(delta < 0);
>  			DBG_BUGON(!ctx->e.length);
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