[PATCH v2] erofs-utils: lib: validate algorithm for encoded extents

[Yifan Zhao]

Hi Utkal Singh,
Thank you for your contributions and the recent fixes.
To help us manage the review process more effectively and avoid 
confusion with duplicate emails,
could you please consolidate these random fixes into a *single patch 
series with a cover letter*in the future?
This allows us to track the entire set of changes in one thread.
Additionally, please follow these conventions for follow-ups:

 1. *Versioning:*If you modify a patch based on review feedback, please
    increment the version prefix (e.g., v2, v3) in the subject line.
 2. *Resends:*If you are simply resending a patch without changes (e.g.,
    to bump it), please add a *RESEND*prefix to the subject line instead
    of treating it as a new version.

This will greatly help in tracking which patches need to be merged.
Regarding backporting patches to the kernel, please refer to commit 
ee2709 in the erofs-utils repository for the preferred commit message 
format.
Specifically, please use square brackets [] to describe any 
modifications you made to the source kernel commit during the backport 
process.
[ Gao may follow up with additional workflow details if needed. ]
Thanks again for your help.

Yifan Zhao


On 3/15/2026 10:22 PM, Utkal Singh wrote:
> Encoded extents use fmt field as algorithm index without checking
> available_compr_algs bitmask. The non-encoded path already has this
> check but the encoded extent path in z_erofs_map_blocks_ext() was
> missing equivalent validation.
>
> Add available_compr_algs consistency check for encoded extents,
> following kernel commit 131897c65e2b.
>
> Signed-off-by: Utkal Singh<singhutkal015 at gmail.com>
> ---
>   lib/zmap.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/lib/zmap.c b/lib/zmap.c
> index 0e7af4e..a8d1ca6 100644
> --- a/lib/zmap.c
> +++ b/lib/zmap.c
> @@ -630,8 +630,17 @@ static int z_erofs_map_blocks_ext(struct erofs_inode *vi,
>   			if (map->m_plen & Z_EROFS_EXTENT_PLEN_PARTIAL)
>   				map->m_flags |= EROFS_MAP_PARTIAL_REF;
>   			map->m_plen &= Z_EROFS_EXTENT_PLEN_MASK;
> -			if (fmt)
> -				map->m_algorithmformat = fmt - 1;
> +			if (fmt) {
> +				unsigned int afmt = fmt - 1;
> +
> +				if (afmt >= Z_EROFS_COMPRESSION_MAX ||
> +				    !(sbi->available_compr_algs & (1 << afmt))) {
> +					erofs_err("unknown algorithm %u for encoded extent, nid %llu",
> +						  afmt, vi->nid | 0ULL);
> +					return -EOPNOTSUPP;
> +				}
> +				map->m_algorithmformat = afmt;
> +			}
>   			else if (interlaced && !((map->m_pa | map->m_plen) & bmask))
>   				map->m_algorithmformat =
>   					Z_EROFS_COMPRESSION_INTERLACED;
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