[net-next,1/2] fib_trie: Avoid NULL pointer if local table is not allocated

The function fib_unmerge assumed the local table had already been
allocated.  If that is not the case however when custom rules are applied
then this can result in a NULL pointer dereference.

In order to prevent this we must check the value of the local table pointer
and if it is NULL simply return 0 as there is no local table to separate
from the main.

Fixes: 0ddcf43d5 ("ipv4: FIB Local/MAIN table collapse")
Reported-by: Madhu Challa <challa@noironetworks.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
---
 net/ipv4/fib_frontend.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)


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I verified it. Looking good. Thanks a lot !

On Thu, Mar 12, 2015 at 2:46 PM, Alexander Duyck
<alexander.h.duyck@redhat.com> wrote:
> The function fib_unmerge assumed the local table had already been
> allocated.  If that is not the case however when custom rules are applied
> then this can result in a NULL pointer dereference.
>
> In order to prevent this we must check the value of the local table pointer
> and if it is NULL simply return 0 as there is no local table to separate
> from the main.
>
> Fixes: 0ddcf43d5 ("ipv4: FIB Local/MAIN table collapse")
> Reported-by: Madhu Challa <challa@noironetworks.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
> ---
>  net/ipv4/fib_frontend.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index c1caf9d..e5b6b05 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -156,9 +156,12 @@ int fib_unmerge(struct net *net)
>  {
>         struct fib_table *old, *new;
>
> +       /* attempt to fetch local table if it has been allocated */
>         old = fib_get_table(net, RT_TABLE_LOCAL);
> -       new = fib_trie_unmerge(old);
> +       if (!old)
> +               return 0;
>
> +       new = fib_trie_unmerge(old);
>         if (!new)
>                 return -ENOMEM;
>
>
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