Subject: Re: [PATCH 2/2] net: qrtr: ns: Limit the maximum lookups per socket

From: Simon Horman <[email-masked]>
Date: Fri, 27 Mar 2026 10:07:09 +0000

On Wed, Mar 25, 2026 at 04:14:15PM +0530, Manivannan Sadhasivam wrote:
> Current code does no bound checking on the number of lookups a client can
> perform per socket. Though the code restricts the lookups to local clients,
> there is still a possibility of a malicious local client sending a flood of
> NEW_LOOKUP messages over the same socket.
> 
> Fix this issue by limiting the maximum number of lookups to 64 per socket.
> Note that, limit of 64 is chosen based on the current platform
> requirements. If requirement changes in the future, this limit can be
> increased.
> 
> Cc: [email-masked]
> Fixes: 0c2204a4ad71 ("net: qrtr: Migrate nameservice to kernel from userspace")
> Signed-off-by: Manivannan Sadhasivam <[email-masked]>
> ---
>  net/qrtr/ns.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/net/qrtr/ns.c b/net/qrtr/ns.c
> index fb4e8a2d370d..707fde809939 100644
> --- a/net/qrtr/ns.c
> +++ b/net/qrtr/ns.c
> @@ -70,10 +70,11 @@ struct qrtr_node {
>  	u32 server_count;
>  };
>  
> -/* Max server limit is chosen based on the current platform requirements. If the
> - * requirement changes in the future, this value can be increased.
> +/* Max server, lookup limits are chosen based on the current platform requirements.
> + * If the requirement changes in the future, these values can be increased.
>   */
>  #define QRTR_NS_MAX_SERVERS 256
> +#define QRTR_NS_MAX_LOOKUPS 64
>  
>  static struct qrtr_node *node_get(unsigned int node_id)
>  {
> @@ -545,11 +546,24 @@ static int ctrl_cmd_new_lookup(struct sockaddr_qrtr *from,
>  	struct qrtr_node *node;
>  	unsigned long node_idx;
>  	unsigned long srv_idx;
> +	u8 count = 0;
>  
>  	/* Accept only local observers */
>  	if (from->sq_node != qrtr_ns.local_node)
>  		return -EINVAL;
>  
> +	/* Make sure the client performs only maximum allowed lookups */
> +	list_for_each_entry(lookup, &qrtr_ns.lookups, li) {
> +		if (lookup->sq.sq_node == from->sq_node &&
> +		    lookup->sq.sq_port == from->sq_port)
> +			count++;

This feels like it could get quite expensive.
If many lookups are added, it feels like it may be O(n^2).

Is this something that has been considered?

> +	}
> +
> +	if (count >= QRTR_NS_MAX_LOOKUPS) {
> +		pr_err_ratelimited("QRTR client node exceeds max lookup limit!\n");
> +		return -ENOSPC;
> +	}
> +
>  	lookup = kzalloc_obj(*lookup);
>  	if (!lookup)
>  		return -ENOMEM;
> -- 
> 2.51.0
>