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

From: Firo Yang <[email-masked]>
Date: Sun, 7 Jun 2015 14:01:29 +0800

On Sat, Jun 06, 2015 at 05:05:04AM -0700, Eric Dumazet wrote:
>On Sat, 2015-06-06 at 19:35 +0800, Firo Yang wrote:
>> A smatch warning.
>> When kmem_cache_alloc() failed to alloc memory, a null pointer
>> will be returned. Redeference null pointer will generate
>
>
>Dereferencing a null pointer will crash.
>
>> 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;
>>  
>>  	if (!kv)
>>  		return NULL;
>>  
>>  	/* initialize key vector */
>> +	l = kv->kv;
>>  	l->key = key;
>>  	l->pos = 0;
>>  	l->bits = 0;
>
>Fixes: dc35dbeda3e0 ("fib_trie: Add tnode struct as a container for fields not needed in key_vector")
>Acked-by: Eric Dumazet <[email-masked]>
>
>Thanks.

Hi Eric,
Please discard this useless patch figured out by Alexander Duyck. 
I will send a patch to Smatch for eliminating the negative warning.

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