From ab9dd052e4d0c4d281ceec0b7e410e229beb6fb2 Mon Sep 17 00:00:00 2001 From: Zhu Yi Date: Thu, 4 Mar 2010 18:01:40 +0000 Subject: net: add limit for socket backlog [ Upstream commit 8eae939f1400326b06d0c9afe53d2a484a326871 ] 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 issue is not only for UDP. Any protocols using socket backlog is potentially affected. The patch adds limit for socket backlog so that the backlog size cannot be expanded endlessly. Reported-by: Alex Shi Cc: David Miller Cc: Arnaldo Carvalho de Melo Cc: Alexey Kuznetsov Cc: "Pekka Savola (ipv6)" Cc: Patrick McHardy Cc: Vlad Yasevich Cc: Sridhar Samudrala Cc: Jon Maloy Cc: Allan Stephens Cc: Andrew Hendry Signed-off-by: Zhu Yi Signed-off-by: Eric Dumazet Acked-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/core/sock.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'net') diff --git a/net/core/sock.c b/net/core/sock.c index e1f6f225f012..385d26210818 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -340,8 +340,12 @@ int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested) rc = sk_backlog_rcv(sk, skb); mutex_release(&sk->sk_lock.dep_map, 1, _RET_IP_); - } else - sk_add_backlog(sk, skb); + } else if (sk_add_backlog_limited(sk, skb)) { + bh_unlock_sock(sk); + atomic_inc(&sk->sk_drops); + goto discard_and_relse; + } + bh_unlock_sock(sk); out: sock_put(sk); @@ -1138,6 +1142,7 @@ 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); /* @@ -1541,6 +1546,12 @@ static void __release_sock(struct sock *sk) bh_lock_sock(sk); } while ((skb = sk->sk_backlog.head) != NULL); + + /* + * Doing the zeroing here guarantee we can not loop forever + * while a wild producer attempts to flood us. + */ + sk->sk_backlog.len = 0; } /** @@ -1873,6 +1884,7 @@ void sock_init_data(struct socket *sock, struct sock *sk) sk->sk_allocation = GFP_KERNEL; sk->sk_rcvbuf = sysctl_rmem_default; sk->sk_sndbuf = sysctl_wmem_default; + sk->sk_backlog.limit = sk->sk_rcvbuf << 1; sk->sk_state = TCP_CLOSE; sk_set_socket(sk, sock); -- cgit v1.2.3