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Date: Sat, 25 Mar 2017 01:10:57 +0100
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Cc: Eric Dumazet <edumazet@...gle.com>,
Andrey Konovalov <andreyknvl@...gle.com>,
"David S. Miller" <davem@...emloft.net>,
Alexey Kuznetsov <kuznet@....inr.ac.ru>,
James Morris <jmorris@...ei.org>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
Patrick McHardy <kaber@...sh.net>, netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Vasily Kulikov <segoon@...nwall.com>
Subject: Re: Linux kernel ping socket / AF_LLC connect() sin_family race
On Fri, Mar 24, 2017 at 03:21:06PM -0700, Eric Dumazet wrote:
> Looks easy enough to fix ?
Oh. Probably. Thanks. Need to test, but I guess you already did?
> diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
> index
> 2af6244b83e27ae384e96cf071c10c5a89674804..ccfbce13a6333a65dab64e4847dd510dfafb1b43
> 100644
> --- a/net/ipv4/ping.c
> +++ b/net/ipv4/ping.c
> @@ -156,17 +156,18 @@ int ping_hash(struct sock *sk)
> void ping_unhash(struct sock *sk)
> {
> struct inet_sock *isk = inet_sk(sk);
> +
> pr_debug("ping_unhash(isk=%p,isk->num=%u)\n", isk, isk->inet_num);
> + write_lock_bh(&ping_table.lock);
> if (sk_hashed(sk)) {
> - write_lock_bh(&ping_table.lock);
> hlist_nulls_del(&sk->sk_nulls_node);
> sk_nulls_node_init(&sk->sk_nulls_node);
> sock_put(sk);
> isk->inet_num = 0;
> isk->inet_sport = 0;
> sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
> - write_unlock_bh(&ping_table.lock);
> }
> + write_unlock_bh(&ping_table.lock);
> }
> EXPORT_SYMBOL_GPL(ping_unhash);
FWIW, in Pavel's original implementation for 2.4.32 (unused), this was:
static void ping_v4_unhash(struct sock *sk)
{
DEBUG(("ping_v4_unhash(sk=%p,sk->num=%u)\n", sk, sk->num));
write_lock_bh(&ping_hash_lock);
if (sk->pprev) {
if (sk->next)
sk->next->pprev = sk->pprev;
*sk->pprev = sk->next;
sk->pprev = NULL;
sk->num = 0;
sock_prot_dec_use(sk->prot);
__sock_put(sk);
}
write_unlock_bh(&ping_hash_lock);
}
Looks like the erroneous optimization (not expecting concurrent activity
on the same socket?) was introduced during conversion to 2.6's hlists.
So far this cursed function had 3 bugs, two of them security (including
this one) and one probably benign (or if not, then effectively a subset
of this bug as it performed some unneeded / stale debugging work before
acquiring the lock), with all 3 introduced in forward-porting. Maybe
the nature of forward-porting activity makes people relatively
inattentive ("compiles with the new interfaces and still works? must be
correct"), compared to when writing new code.
Anyhow, I share some responsibility for this mess, for having advocated
this patch being forward-ported and merged back then. I still like
having this functionality and its userspace security benefits... but I
don't like the kernel bugs.
Alexander
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