This is a note to let you know that I've just added the patch titled neigh: fix possible DoS due to net iface start/stop loop to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: neigh-fix-possible-dos-due-to-net-iface-start-stop-l.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 4deaacb992f2bf7477ec740e048ece18557edac8 Author: Denis V. Lunev <den@xxxxxxxxxx> Date: Thu Aug 11 18:20:11 2022 +0300 neigh: fix possible DoS due to net iface start/stop loop [ Upstream commit 66ba215cb51323e4e55e38fd5f250e0fae0cbc94 ] Normal processing of ARP request (usually this is Ethernet broadcast packet) coming to the host is looking like the following: * the packet comes to arp_process() call and is passed through routing procedure * the request is put into the queue using pneigh_enqueue() if corresponding ARP record is not local (common case for container records on the host) * the request is processed by timer (within 80 jiffies by default) and ARP reply is sent from the same arp_process() using NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED condition (flag is set inside pneigh_enqueue()) And here the problem comes. Linux kernel calls pneigh_queue_purge() which destroys the whole queue of ARP requests on ANY network interface start/stop event through __neigh_ifdown(). This is actually not a problem within the original world as network interface start/stop was accessible to the host 'root' only, which could do more destructive things. But the world is changed and there are Linux containers available. Here container 'root' has an access to this API and could be considered as untrusted user in the hosting (container's) world. Thus there is an attack vector to other containers on node when container's root will endlessly start/stop interfaces. We have observed similar situation on a real production node when docker container was doing such activity and thus other containers on the node become not accessible. The patch proposed doing very simple thing. It drops only packets from the same namespace in the pneigh_queue_purge() where network interface state change is detected. This is enough to prevent the problem for the whole node preserving original semantics of the code. v2: - do del_timer_sync() if queue is empty after pneigh_queue_purge() v3: - rebase to net tree Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Cc: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Jakub Kicinski <kuba@xxxxxxxxxx> Cc: Paolo Abeni <pabeni@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: David Ahern <dsahern@xxxxxxxxxx> Cc: Yajun Deng <yajun.deng@xxxxxxxxx> Cc: Roopa Prabhu <roopa@xxxxxxxxxx> Cc: Christian Brauner <brauner@xxxxxxxxxx> Cc: netdev@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx> Cc: Alexander Mikhalitsyn <alexander.mikhalitsyn@xxxxxxxxxxxxx> Cc: Konstantin Khorenko <khorenko@xxxxxxxxxxxxx> Cc: kernel@xxxxxxxxxx Cc: devel@xxxxxxxxxx Investigated-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@xxxxxxxxxxxxx> Signed-off-by: Denis V. Lunev <den@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 358e84af0210b..8af9761768e00 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -222,14 +222,23 @@ static int neigh_del_timer(struct neighbour *n) return 0; } -static void pneigh_queue_purge(struct sk_buff_head *list) +static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net) { + unsigned long flags; struct sk_buff *skb; - while ((skb = skb_dequeue(list)) != NULL) { - dev_put(skb->dev); - kfree_skb(skb); + spin_lock_irqsave(&list->lock, flags); + skb = skb_peek(list); + while (skb != NULL) { + struct sk_buff *skb_next = skb_peek_next(skb, list); + if (net == NULL || net_eq(dev_net(skb->dev), net)) { + __skb_unlink(skb, list); + dev_put(skb->dev); + kfree_skb(skb); + } + skb = skb_next; } + spin_unlock_irqrestore(&list->lock, flags); } static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev) @@ -295,9 +304,9 @@ int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev) write_lock_bh(&tbl->lock); neigh_flush_dev(tbl, dev); pneigh_ifdown_and_unlock(tbl, dev); - - del_timer_sync(&tbl->proxy_timer); - pneigh_queue_purge(&tbl->proxy_queue); + pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev)); + if (skb_queue_empty_lockless(&tbl->proxy_queue)) + del_timer_sync(&tbl->proxy_timer); return 0; } EXPORT_SYMBOL(neigh_ifdown); @@ -1609,7 +1618,7 @@ int neigh_table_clear(int index, struct neigh_table *tbl) /* It is not clean... Fix it to unload IPv6 module safely */ cancel_delayed_work_sync(&tbl->gc_work); del_timer_sync(&tbl->proxy_timer); - pneigh_queue_purge(&tbl->proxy_queue); + pneigh_queue_purge(&tbl->proxy_queue, NULL); neigh_ifdown(tbl, NULL); if (atomic_read(&tbl->entries)) pr_crit("neighbour leakage\n");