diff mbox

[net] udp: fix dst races with multicast early demux

Message ID 1438424073.2748.28.camel@edumazet-glaptop2.roam.corp.google.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Aug. 1, 2015, 10:14 a.m. UTC 
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 !

 net/ipv4/udp.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)



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Comments

David Miller Aug. 4, 2015, 5:20 a.m. UTC | #1 
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!
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diff mbox

Patch

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)