Re: [PATCH net] net: dsa: validate source trunk against lags_len

[Dawid Osuchowski <dawid.osuchowski@linux.intel.com>]

On 2025-07-31 7:35 AM, Luke Howard wrote:
> A DSA frame with an invalid source trunk ID could cause an out-of-bounds read
> access of dst->lags.
> 
> This patch adds a check to dsa_lag_by_id() to validate the LAG ID is not zero,

checkpatch is saying this line is not wrapped at 75 columns

> and is less than or equal to dst->lags_len. (The LAG ID is derived by adding
> one to the source trunk ID.)
> 
> Note: this is in the fast path for any frames within a trunk.
> 
> Signed-off-by: Luke Howard <lukeh@padl.com>

Reviewed-by: Dawid Osuchowski <dawid.osuchowski@linux.intel.com>

Thanks,
Dawid

> ---
>   include/net/dsa.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/include/net/dsa.h b/include/net/dsa.h
> index 2e148823c366c..67672c5ff22e5 100644
> --- a/include/net/dsa.h
> +++ b/include/net/dsa.h
> @@ -180,6 +180,9 @@ struct dsa_switch_tree {
>   static inline struct dsa_lag *dsa_lag_by_id(struct dsa_switch_tree *dst,
>   					    unsigned int id)
>   {
> +	if (unlikely(id == 0 || id > dst->lags_len))
> +		return NULL;
> +
>   	/* DSA LAG IDs are one-based, dst->lags is zero-based */
>   	return dst->lags[id - 1];
>   }