Message ID | 1438424073.2748.28.camel@edumazet-glaptop2.roam.corp.google.com |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Sat, 01 Aug 2015 12:14:33 +0200 > From: Eric Dumazet <edumazet@google.com> > > Multicast dst are not cached. They carry DST_NOCACHE. > > As mentioned in commit f8864972126899 ("ipv4: fix dst race in > sk_dst_get()"), these dst need special care before caching them > into a socket. > > Caching them is allowed only if their refcnt was not 0, ie we > must use atomic_inc_not_zero() > > Also, we must use READ_ONCE() to fetch sk->sk_rx_dst, as mentioned > in commit d0c294c53a771 ("tcp: prevent fetching dst twice in early demux > code") > > Fixes: 421b3885bf6d ("udp: ipv4: Add udp early demux") > Signed-off-by: Eric Dumazet <edumazet@google.com> > Reported-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz> > Reported-by: Alex Gartrell <agartrell@fb.com> > Cc: Michal Kubeček <mkubecek@suse.cz> > --- > David : I will be on vacation for following 7 days, no internet access. > Please wait for tests done by Gregory & Alex before merging this ? > Thanks ! Now that this has been tested by Gregory, applied and queued up for -stable thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 83aa604f9273..1b8c5ba7d5f7 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1995,12 +1995,19 @@ void udp_v4_early_demux(struct sk_buff *skb) skb->sk = sk; skb->destructor = sock_efree; - dst = sk->sk_rx_dst; + dst = READ_ONCE(sk->sk_rx_dst); if (dst) dst = dst_check(dst, 0); - if (dst) - skb_dst_set_noref(skb, dst); + if (dst) { + /* DST_NOCACHE can not be used without taking a reference */ + if (dst->flags & DST_NOCACHE) { + if (likely(atomic_inc_not_zero(&dst->__refcnt))) + skb_dst_set(skb, dst); + } else { + skb_dst_set_noref(skb, dst); + } + } } int udp_rcv(struct sk_buff *skb)