Subject: Re: [RFC PATCH] net: cgroup: null ptr dereference in netprio cgroup during init

From: Gao feng <[email-masked]>
Date: Wed, 18 Jul 2012 09:59:39 +0800

于 2012年07月18日 08:33, John Fastabend 写道:
> When the netprio cgroup is built in the kernel cgroup_init will call
> cgrp_create which eventually calls update_netdev_tables. This is
> being called before do_initcalls() so a null ptr dereference occurs
> on init_net.
> 
> This patch adds a check on init_net.count to verify the structure
> has been initialized. The failure was introduced here,
> 
> commit ef209f15980360f6945873df3cd710c5f62f2a3e
> Author: Gao feng <[email-masked]>
> Date:   Wed Jul 11 21:50:15 2012 +0000
> 
>     net: cgroup: fix access the unallocated memory in netprio cgroup
> 
> Tested with ping with netprio_cgroup as a module and built in.
> 
> Marked RFC for now I think DaveM might have a reason why this needs
> some improvement.
> 
> Reported-by: Mark Rustad <[email-masked]>
> Cc: Neil Horman <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> Cc: Gao feng <[email-masked]>
> Signed-off-by: John Fastabend <[email-masked]>
> ---
> 
>  net/core/netprio_cgroup.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
> index b2e9caa..e9fd7fd 100644
> --- a/net/core/netprio_cgroup.c
> +++ b/net/core/netprio_cgroup.c
> @@ -116,6 +116,9 @@ static int update_netdev_tables(void)
>  	u32 max_len;
>  	struct netprio_map *map;

Thanks John.
It's my mistake.

Can we make sure init_net.count is zero here?
I can't find some places to initialize it to zero.

>  
> +	if (!atomic_read(&init_net.count))
> +		return ret;
> +
>  	rtnl_lock();
>  	max_len = atomic_read(&max_prioidx) + 1;
>  	for_each_netdev(&init_net, dev) {
> 
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