Subject: Re: [PATCH] fib_trie: Fix potential null pointer dereference

From: walter harms <[email-masked]>
Date: Sat, 06 Jun 2015 15:39:38 +0200

Am 06.06.2015 13:35, schrieb Firo Yang:
> A smatch warning.
> When kmem_cache_alloc() failed to alloc memory, a null pointer
> will be returned. Redeference null pointer will generate
> an unnecessary oops. So, use it after check.
> 
> Signed-off-by: Firo Yang <[email-masked]>
> ---
>  net/ipv4/fib_trie.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 01bce15..34094c7 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -326,12 +326,13 @@ static inline void empty_child_dec(struct key_vector *n)
>  static struct key_vector *leaf_new(t_key key, struct fib_alias *fa)
>  {
>  	struct tnode *kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
> -	struct key_vector *l = kv->kv;
> +	struct key_vector *l;

It is a good custom to have action and check close together, so this may be more
obvious for future readers:
	struct tnode *kv;
	struct key_vector *l;

        kv = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
  	if (!kv)
  		return NULL;

re,
 wh

>  	/* initialize key vector */
> +	l = kv->kv;
>  	l->key = key;
>  	l->pos = 0;
>  	l->bits = 0;