From: Denis V. Lunev den@openvz.org
[ 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@davemloft.net Cc: Eric Dumazet edumazet@google.com Cc: Jakub Kicinski kuba@kernel.org Cc: Paolo Abeni pabeni@redhat.com Cc: Daniel Borkmann daniel@iogearbox.net Cc: David Ahern dsahern@kernel.org Cc: Yajun Deng yajun.deng@linux.dev Cc: Roopa Prabhu roopa@nvidia.com Cc: Christian Brauner brauner@kernel.org Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Alexey Kuznetsov kuznet@ms2.inr.ac.ru Cc: Alexander Mikhalitsyn alexander.mikhalitsyn@virtuozzo.com Cc: Konstantin Khorenko khorenko@virtuozzo.com Cc: kernel@openvz.org Cc: devel@openvz.org Investigated-by: Alexander Mikhalitsyn alexander.mikhalitsyn@virtuozzo.com Signed-off-by: Denis V. Lunev den@openvz.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/neighbour.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-)
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");