Re: [PATCH net] ipv4: free net->ipv4.sysctl_local_reserved_ports after unregister_net_sysctl_table()

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 5/21/26 8:21 PM, Eric Dumazet wrote:
> ipv4_sysctl_exit_net() is currently freeing net->ipv4.sysctl_local_reserved_ports
> too soon.
>
> Only after unregister_net_sysctl_table() we can be sure no threads can possibly
> use the sysctls, including /proc/sys/net/ipv4/ip_local_reserved_ports.
>
> Fixes: 122ff243f5f1 ("ipv4: make ip_local_reserved_ports per netns")
> Reported-by: Ji'an Zhou <eilaimemedsnaimel@gmail.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>   net/ipv4/sysctl_net_ipv4.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index d8bdb1bdbff17ab52fe969b93ce13673e88c05a4..c0e85cc171aec099fd5d4897b1a623dd27eaee08 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -1705,10 +1705,10 @@ static __net_exit void ipv4_sysctl_exit_net(struct net *net)
>   {
>   	const struct ctl_table *table;
>   
> -	kfree(net->ipv4.sysctl_local_reserved_ports);
>   	table = net->ipv4.ipv4_hdr->ctl_table_arg;
>   	unregister_net_sysctl_table(net->ipv4.ipv4_hdr);
>   	kfree(table);
> +	kfree(net->ipv4.sysctl_local_reserved_ports);
>   }
>   
>   static __net_initdata struct pernet_operations ipv4_sysctl_ops = {


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>


If there are still processes in the namespace, the netns refcnt cannot 
become 0,

so I think it should be: first open 
/proc/sys/net/ipv4/ip_local_reserved_ports, then pass

the fd to another process outside the netns? Maybe SCM_RIGHTS is used?