| Message ID | 1267176464-426-1-git-send-email-yi.zhu@intel.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Zhu Yi <yi.zhu@intel.com> Date: Fri, 26 Feb 2010 17:27:44 +0800 > We got system OOM while running some UDP netperf testing on the loopback > device. The case is multiple senders sent stream UDP packets to a single > receiver via loopback on local host. Of course, the receiver is not able > to handle all the packets in time. But we surprisingly found that these > packets were not discarded due to the receiver's sk->sk_rcvbuf limit. > Instead, they are kept queuing to sk->sk_backlog and finally ate up all > the memory. We believe this is a secure hole that a none privileged user > can crash the system. > > The root cause for this problem is, when the receiver is doing > __release_sock() (i.e. after userspace recv, kernel udp_recvmsg -> > skb_free_datagram_locked -> release_sock), it moves skbs from backlog to > sk_receive_queue with the softirq enabled. In the above case, multiple > busy senders will almost make it an endless loop. The skbs in the > backlog end up eat all the system memory. > > The patch fixed this problem by adding accounting for the socket > backlog. So that the backlog size can be restricted by protocol's choice > (i.e. UDP). > > Reported-by: Alex Shi <alex.shi@intel.com> > Cc: David Miller <davem@davemloft.net> > Cc: Eric Dumazet <eric.dumazet@gmail.com> > Signed-off-by: Zhu Yi <yi.zhu@intel.com> So remind me why TCP, or any other non-UDP protocol, won't intrinsically have this problem too? It seems pretty trivial to do with any protocol, especially remotely, with a packet generator. The code in TCP, for example, which queues to the backlog, doesn't care about sequence numbers or anything like that. So you could spray a machine with the same TCP frame over and over again, as fast as possible, as long as it matches the socket identity. And in this way fill up the backlog endlessly and OOM the system. -- 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
On Fri, 2010-02-26 at 20:05 +0800, David Miller wrote: > So remind me why TCP, or any other non-UDP protocol, won't > intrinsically have this problem too? If TCP ACKs are not received, the (closed) remote window prevents the TCP sender to send more frames. > It seems pretty trivial to do with any protocol, especially remotely, > with a packet generator. The code in TCP, for example, which queues > to the backlog, doesn't care about sequence numbers or anything like > that. > > So you could spray a machine with the same TCP frame over and over > again, as fast as possible, as long as it matches the socket identity. > > And in this way fill up the backlog endlessly and OOM the system. Yeah, I only considered about the normal case, that is the TCP frames are built and managed in the kernel. If a user does frame generation himself, yes, the same problem could happen potentially for all protocols using backlog. Thanks, -yi -- 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
From: Zhu Yi <yi.zhu@intel.com> Date: Mon, 01 Mar 2010 10:08:48 +0800 > Yeah, I only considered about the normal case, that is the TCP frames > are built and managed in the kernel. You're not even considering the kernel case completely. It's just as easy to modify the kernel to maliciously send frames in this way. > If a user does frame generation himself, yes, the same problem could > happen potentially for all protocols using backlog. We need the protection for every protocol, please implement your changes this way. 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/include/net/sock.h b/include/net/sock.h index 3f1a480..9f6893b 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -253,6 +253,7 @@ struct sock { struct { struct sk_buff *head; struct sk_buff *tail; + int len; } sk_backlog; wait_queue_head_t *sk_sleep; struct dst_entry *sk_dst_cache; @@ -583,11 +584,22 @@ static inline void sk_add_backlog(struct sock *sk, struct sk_buff *skb) sk->sk_backlog.tail->next = skb; sk->sk_backlog.tail = skb; } + sk->sk_backlog.len += skb->truesize; skb->next = NULL; } +static inline int sk_add_backlog_limited(struct sock *sk, struct sk_buff *skb) +{ + if (sk->sk_backlog.len >= 2 * sk->sk_rcvbuf) + return -ENOBUFS; + + sk_add_backlog(sk, skb); + return 0; +} + static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb) { + sk->sk_backlog.len -= skb->truesize; return sk->sk_backlog_rcv(sk, skb); } diff --git a/net/core/sock.c b/net/core/sock.c index e1f6f22..82228ef 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1138,6 +1138,7 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority) sock_lock_init(newsk); bh_lock_sock(newsk); newsk->sk_backlog.head = newsk->sk_backlog.tail = NULL; + newsk->sk_backlog.len = 0; atomic_set(&newsk->sk_rmem_alloc, 0); /* diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index f0126fd..7bb4568 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1372,8 +1372,10 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb) bh_lock_sock(sk); if (!sock_owned_by_user(sk)) rc = __udp_queue_rcv_skb(sk, skb); - else - sk_add_backlog(sk, skb); + else if (sk_add_backlog_limited(sk, skb)) { + bh_unlock_sock(sk); + goto drop; + } bh_unlock_sock(sk); return rc; diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 69ebdbe..e4a8645 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -584,16 +584,19 @@ static void flush_stack(struct sock **stack, unsigned int count, bh_lock_sock(sk); if (!sock_owned_by_user(sk)) udpv6_queue_rcv_skb(sk, skb1); - else - sk_add_backlog(sk, skb1); + else if (sk_add_backlog_limited(sk, skb1)) { + bh_unlock_sock(sk); + goto drop; + } bh_unlock_sock(sk); - } else { - atomic_inc(&sk->sk_drops); - UDP6_INC_STATS_BH(sock_net(sk), - UDP_MIB_RCVBUFERRORS, IS_UDPLITE(sk)); - UDP6_INC_STATS_BH(sock_net(sk), - UDP_MIB_INERRORS, IS_UDPLITE(sk)); + continue; } +drop: + atomic_inc(&sk->sk_drops); + UDP6_INC_STATS_BH(sock_net(sk), + UDP_MIB_RCVBUFERRORS, IS_UDPLITE(sk)); + UDP6_INC_STATS_BH(sock_net(sk), + UDP_MIB_INERRORS, IS_UDPLITE(sk)); } } /* @@ -756,8 +759,11 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable, bh_lock_sock(sk); if (!sock_owned_by_user(sk)) udpv6_queue_rcv_skb(sk, skb); - else - sk_add_backlog(sk, skb); + else if (sk_add_backlog_limited(sk, skb)) { + bh_unlock_sock(sk); + sock_put(sk); + goto discard; + } bh_unlock_sock(sk); sock_put(sk); return 0;
We got system OOM while running some UDP netperf testing on the loopback device. The case is multiple senders sent stream UDP packets to a single receiver via loopback on local host. Of course, the receiver is not able to handle all the packets in time. But we surprisingly found that these packets were not discarded due to the receiver's sk->sk_rcvbuf limit. Instead, they are kept queuing to sk->sk_backlog and finally ate up all the memory. We believe this is a secure hole that a none privileged user can crash the system. The root cause for this problem is, when the receiver is doing __release_sock() (i.e. after userspace recv, kernel udp_recvmsg -> skb_free_datagram_locked -> release_sock), it moves skbs from backlog to sk_receive_queue with the softirq enabled. In the above case, multiple busy senders will almost make it an endless loop. The skbs in the backlog end up eat all the system memory. The patch fixed this problem by adding accounting for the socket backlog. So that the backlog size can be restricted by protocol's choice (i.e. UDP). Reported-by: Alex Shi <alex.shi@intel.com> Cc: David Miller <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Zhu Yi <yi.zhu@intel.com> --- V2: remove atomic operation for sk_backlog.len limit UDP backlog size to 2*sk->sk_rcvbuf -- 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