netdev - Re: [PATCH] net: fix for a race condition in the inet frag code

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]

Date:	Mon, 3 Mar 2014 15:40:26 +0100
From:	Florian Westphal <fw@...len.de>
To:	Nikolay Aleksandrov <nikolay@...hat.com>
Cc:	netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] net: fix for a race condition in the inet frag code

Nikolay Aleksandrov <nikolay@...hat.com> wrote:
> I stumbled upon this very serious bug while hunting for another one,
> it's a very subtle race condition between inet_frag_evictor,
> inet_frag_intern and the IPv4/6 frag_queue and expire functions (basically
> the users of inet_frag_kill/inet_frag_put).
> What happens is that after a fragment has been added to the hash chain but
> before it's been added to the lru_list (inet_frag_lru_add), it may get
> deleted (either by an expired timer if the system load is high or the
> timer sufficiently low, or by the fraq_queue function for different
> reasons) before it's added to the lru_list

Sorry.  Not following here, see below.

> diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
> index bb075fc9a14f..322dcebfc588 100644
> --- a/net/ipv4/inet_fragment.c
> +++ b/net/ipv4/inet_fragment.c
> @@ -278,9 +278,10 @@ static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf,
>  
>  	atomic_inc(&qp->refcnt);
>  	hlist_add_head(&qp->list, &hb->chain);
> +	inet_frag_lru_add(nf, qp);
>  	spin_unlock(&hb->chain_lock);
>  	read_unlock(&f->lock);

If I understand correctly your're saying that qp can be free'd on
another/cpu timer right after dropping the locks.  But how is it
possible?

->refcnt is bumped above when arming the timer (before dropping chain
lock), so even if the frag_expire timer fires instantly it should not
free qp.

What am I missing?

Thanks,
Florian
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html