error path in __ip_vs_init()

error path in __ip_vs_init()

[Tetsuo Handa]

Line 1880 cannot become true because net_generic() cannot return NULL.
Redundant check?

include/net/netns/generic.h:
 34 static inline void *net_generic(const struct net *net, int id)
 35 {
 36         struct net_generic *ng;
 37         void *ptr;
 38 
 39         rcu_read_lock();
 40         ng = rcu_dereference(net->gen);
 41         BUG_ON(id == 0 || id > ng->len);
 42         ptr = ng->ptr[id - 1];
 43         rcu_read_unlock();
 44 
 45         BUG_ON(!ptr);
 46         return ptr;
 47 }

net/netfilter/ipvs/ip_vs_core.c:
1875 static int __net_init __ip_vs_init(struct net *net)
1876 {
1877         struct netns_ipvs *ipvs;
1878 
1879         ipvs = net_generic(net, ip_vs_net_id);
1880         if (ipvs == NULL)
1881                 return -ENOMEM;

Re: error path in __ip_vs_init()

[Eric Dumazet]

On Sat, 2012-04-14 at 19:42 +0900, Tetsuo Handa wrote:
> Line 1880 cannot become true because net_generic() cannot return NULL.
> Redundant check?
> 
> include/net/netns/generic.h:
>  34 static inline void *net_generic(const struct net *net, int id)
>  35 {
>  36         struct net_generic *ng;
>  37         void *ptr;
>  38 
>  39         rcu_read_lock();
>  40         ng = rcu_dereference(net->gen);
>  41         BUG_ON(id == 0 || id > ng->len);
>  42         ptr = ng->ptr[id - 1];
>  43         rcu_read_unlock();
>  44 
>  45         BUG_ON(!ptr);
>  46         return ptr;
>  47 }
> 
> net/netfilter/ipvs/ip_vs_core.c:
> 1875 static int __net_init __ip_vs_init(struct net *net)
> 1876 {
> 1877         struct netns_ipvs *ipvs;
> 1878 
> 1879         ipvs = net_generic(net, ip_vs_net_id);
> 1880         if (ipvs == NULL)
> 1881                 return -ENOMEM;
> --

Yep, because the BUG_ON(!ptr) was added very recently :

commit 5ee4433efe99b9f39f6eff5052a177bbcfe72cea
Author: Eric W. Biederman <ebiederm@xmission.com>
Date:   Thu Jan 26 14:02:55 2012 +0000

    netns: Fail conspicously if someone uses net_generic at an inappropriate time.
    
    By definition net_generic should never be called when it can return
    NULL.  Fail conspicously with a BUG_ON to make it clear when people mess
    up that a NULL return should never happen.
    
    Recently there was a bug in the CAIF subsystem where it was registered
    with register_pernet_device instead of register_pernet_subsys.  It was
    erroneously concluded that net_generic could validly return NULL and
    that net_assign_generic was buggy (when it was just inefficient).
    Hopefully this BUG_ON will prevent people to coming to similar erroneous
    conclusions in the futrue.
    
    Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    Tested-by: Sasha Levin <levinsasha928@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>


So feel free to submit a patch ;)