Re: [PATCH net] sfc: fix NULL pointer dereference in efx_tc_flower_replace_foreign()

[Edward Cree <ecree.xilinx@gmail.com>]

On 14/10/2026 15:58, Rand Deeb wrote:
> efx_tc_flower_replace_foreign() walks the rule's actions with an 'act'
> cursor. After a redirect action it adds the action set to the rule and
> sets the cursor to NULL:
> 
> 	list_add_tail(&act->list, &rule->acts.list);
> 	act = NULL;
> 	if (fa->id == FLOW_ACTION_REDIRECT)
> 		break; /* end of the line */
> 
> The break only leaves the switch statement, so flow_action_for_each()
> carries on with the next action while act is NULL. A following redirect
> or mirred action then does "save = *act", and a following tunnel decap
> action passes act to efx_tc_flower_action_order_ok(), which reads
> act->decap. Both dereference a NULL pointer.
> 
> The loop is missing the check that efx_tc_flower_replace() performs at
> the start of every iteration for the same cursor: reject the rule if an
> action follows a non-pipe action. The foreign variant was added without
> it.
> 
> As a result, a TC flower rule on a tunnel netdevice that redirects to an
> sfc representor and lists another redirect, mirred or tunnel decap
> action after the first redirect causes a kernel NULL pointer
> dereference. It happens in the context of the task adding the filter,
> with efx->tc->mutex held. Adding such a rule requires CAP_NET_ADMIN.
> 
> Add the same check at the top of the action loop in
> efx_tc_flower_replace_foreign(), returning -EINVAL with the same extack
> message as efx_tc_flower_replace(). The release path already copes with
> act being NULL.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 17654d84b47c ("sfc: add offloading of 'foreign' TC (decap) rules")
> Signed-off-by: Rand Deeb <rand.sec96@gmail.com>

Diagnosis and fix look correct to me.
Acked-by: Edward Cree <ecree.xilinx@gmail.com>

Sadly I don't have a working ef100 to test this on.