netdev - Re: [PATCH net] inet: frags: better deal with smp races

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20181108.170235.1217371124928853665.davem@davemloft.net>
Date:   Thu, 08 Nov 2018 17:02:35 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        soukjin.bae@...sung.com
Subject: Re: [PATCH net] inet: frags: better deal with smp races

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed,  7 Nov 2018 22:10:53 -0800

> @@ -204,22 +205,22 @@ static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
>  /* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
>  struct inet_frag_queue *inet_frag_find(struct netns_frags *nf, void *key)
>  {
> -	struct inet_frag_queue *fq;
> +	struct inet_frag_queue *fq, *prev;
>  
>  	if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh)
>  		return NULL;
>  
>  	rcu_read_lock();
>  
> -	fq = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
> -	if (fq) {
> +	prev = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
> +	if (!prev)
> +		fq = inet_frag_create(nf, key, &prev);
> +	if (prev && !IS_ERR(prev)) {
> +		fq = prev;
>  		if (!refcount_inc_not_zero(&fq->refcnt))
>  			fq = NULL;
> -		rcu_read_unlock();
> -		return fq;
>  	}
>  	rcu_read_unlock();
> -
> -	return inet_frag_create(nf, key);
> +	return fq;

GCC is unwilling to see that all paths leading to that final return
statement do in fact set 'fq' one way or another:

net/ipv4/inet_fragment.c: In function ‘inet_frag_find’:
net/ipv4/inet_fragment.c:224:9: warning: ‘fq’ may be used uninitialized in this function [-Wmaybe-uninitialized]

This is with:

gcc (GCC) 8.2.1 20181011 (Red Hat 8.2.1-4)

Please adjust your patch so that the warning is eliminated.

Thanks.