Re: [PATCH net] route: set the deleted fnhe fnhe_daddr to 0 in ip_del_fnhe to fix a race

[David Ahern <dsahern@gmail.com>]

On 3/7/19 11:50 PM, Xin Long wrote:
> The race occurs in __mkroute_output() when 2 threads lookup a dst:
> 
>   CPU A                 CPU B
>   find_exception()
>                         find_exception() [fnhe expires]
>                         ip_del_fnhe() [fnhe is deleted]
>   rt_bind_exception()
> 
> In rt_bind_exception() it will bind a deleted fnhe with the new dst, and
> this dst will get no chance to be freed. It causes a dev defcnt leak and
> consecutive dmesg warnings:
> 
>   unregister_netdevice: waiting for ethX to become free. Usage count = 1
> 
> Especially thinks Jon to identify the issue.
> 
> This patch fixes it by setting fnhe_daddr to 0 in ip_del_fnhe() to stop
> binding the deleted fnhe with a new dst when checking fnhe's fnhe_daddr
> and daddr in rt_bind_exception().
> 
> It works as both ip_del_fnhe() and rt_bind_exception() are protected by
> fnhe_lock and the fhne is freed by kfree_rcu().
> 
> Fixes: deed49df7390 ("route: check and remove route cache when we get route")
> Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/ipv4/route.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 

Reviewed-by: David Ahern <dsahern@gmail.com>