Subject: Re: [PATCH RESEND 1/2] neigh: only allow init_net to change the default neigh_parms

From: Gao feng <[email-masked]>
Date: Thu, 13 Jun 2013 09:17:52 +0800

On 06/12/2013 03:33 PM, Eric W. Biederman wrote:
> Gao feng <[email-masked]> writes:
> 
>> Though we don't export the /proc/sys/net/ipv[4,6]/neigh/default/
>> directory to the un-init_net, but we can still use cmd such as
>> "ip ntable change name arp_cache locktime 129" to change the locktime
>> of default neigh_parms.
>>
>> This patch disallows the un-init_net to find out the neigh_table.parms.
>> So the un-init_net will failed to influence the init_net.
> 
> Interesting...  
> 
> The problem these two patches seek to address seems legit.
> 
> However I disagree with the way you are handling this.
> 
> Outside of the initial network namespace we should return -ENOENT
> instead of -EPERM.  Which would match how we handle sysctls, and I think
> missing neigh table values.  Just not making these global values visible
> seems wise.
> 

Ok, it seems more reasonable.

> The alternative is to use the proper permission test which is
> capable(CAP_SYS_ADMIN) (instead of testing network namespaces) and
> return -EPERM if that fails.  Which would allow processes in other
> network namespaces to change the value if they could otherwise change
> the value.
> 

So you mean the uninitial net namespace can't see these values but it
can change them? it's too strange.
And the thresh/interval are both under default/ too, if we return -ENOENT
for other items, we should also return -ENOENT for them instead of the -EPERM.

> Namespaces are about visibility and there is no need to make an
> exception here.
> 
> Eric
> 
>> Signed-off-by: Gao feng <[email-masked]>
>> ---
>>  net/core/neighbour.c | 25 ++++++++++++++-----------
>>  1 file changed, 14 insertions(+), 11 deletions(-)
>>
>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>> index 5c56b21..e4027ff 100644
>> --- a/net/core/neighbour.c
>> +++ b/net/core/neighbour.c
>> @@ -1418,26 +1418,29 @@ static inline struct neigh_parms *lookup_neigh_parms(struct neigh_table *tbl,
>>  	struct neigh_parms *p;
>>  
>>  	for (p = &tbl->parms; p; p = p->next) {
>> -		if ((p->dev && p->dev->ifindex == ifindex && net_eq(neigh_parms_net(p), net)) ||
>> -		    (!p->dev && !ifindex))
>> +		if (p->dev && p->dev->ifindex == ifindex &&
>> +		    net_eq(neigh_parms_net(p), net))
>>  			return p;
>> +
>> +		if (!p->dev && !ifindex) {
>> +			if (net_eq(net, &init_net))
>> +				return p;
>> +			else
>> +				return ERR_PTR(-EPERM);
>> +		}
>>  	}
>>  
>> -	return NULL;
>> +	return ERR_PTR(-ENOENT);
>>  }
>>  
>>  struct neigh_parms *neigh_parms_alloc(struct net_device *dev,
>>  				      struct neigh_table *tbl)
>>  {
>> -	struct neigh_parms *p, *ref;
>> +	struct neigh_parms *p;
>>  	struct net *net = dev_net(dev);
>>  	const struct net_device_ops *ops = dev->netdev_ops;
>>  
>> -	ref = lookup_neigh_parms(tbl, net, 0);
>> -	if (!ref)
>> -		return NULL;
>> -
>> -	p = kmemdup(ref, sizeof(*p), GFP_KERNEL);
>> +	p = kmemdup(&tbl->parms, sizeof(*p), GFP_KERNEL);
>>  	if (p) {
>>  		p->tbl		  = tbl;
>>  		atomic_set(&p->refcnt, 1);
>> @@ -1999,8 +2002,8 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh)
>>  			ifindex = nla_get_u32(tbp[NDTPA_IFINDEX]);
>>  
>>  		p = lookup_neigh_parms(tbl, net, ifindex);
>> -		if (p == NULL) {
>> -			err = -ENOENT;
>> +		if (IS_ERR(p)) {
>> +			err = PTR_ERR(p);
>>  			goto errout_tbl_lock;
>>  		}
>