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

[Manivannan Sadhasivam]

On Fri, Mar 27, 2026 at 10:07:09AM +0000, Simon Horman wrote:
> 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: stable@xxxxxxxxxxxxxxx
> > Fixes: 0c2204a4ad71 ("net: qrtr: Migrate nameservice to kernel from userspace")
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
> > ---
> >  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).
> 

Lookups are not something that'll happen very often. A client only registers
for the lookup once per service that it depends on. That shouldn't be too
much. And then once lookup is registered, it will be used throughout the
lifetime of the client.

So there is no overhead associated with this check.

- Mani

-- 
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