linux-kernel - Re: [PATCH] ipv4: fib: avoid NULL dereference

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Date:   Fri, 6 Jul 2018 08:49:14 -0600
From:   David Ahern <dsahern@...il.com>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: fib: avoid NULL dereference

On 7/6/18 8:28 AM, Mark Rutland wrote:
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 5bc0c89e81e4..8d98c8162554 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -497,11 +497,11 @@ static void tnode_free(struct key_vector *tn)
>  	struct callback_head *head = &tn_info(tn)->rcu;
>  
>  	while (head) {
> +		tn = container_of(head, struct tnode, rcu)->kv;
> +
>  		head = head->next;
>  		tnode_free_size += TNODE_SIZE(1ul << tn->bits);
>  		node_free(tn);

you are changing tn before the above 2 calls are made on the tn passed in


> -
> -		tn = container_of(head, struct tnode, rcu)->kv;
>  	}
>  
>  	if (tnode_free_size >= PAGE_SIZE * sync_pages) {
>