From 8eae939f1400326b06d0c9afe53d2a484a326871 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 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: 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 --- include/net/sock.h | 15 ++++++++++++++- net/core/sock.c | 16 ++++++++++++++-- 2 files changed, 28 insertions(+), 3 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 6cb1676..2516d76 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -253,6 +253,8 @@ struct sock { struct { struct sk_buff *head; struct sk_buff *tail; + int len; + int limit; } sk_backlog; wait_queue_head_t *sk_sleep; struct dst_entry *sk_dst_cache; @@ -589,7 +591,7 @@ static inline int sk_stream_memory_free(struct sock *sk) return sk->sk_wmem_queued < sk->sk_sndbuf; } -/* The per-socket spinlock must be held here. */ +/* OOB backlog add */ static inline void sk_add_backlog(struct sock *sk, struct sk_buff *skb) { if (!sk->sk_backlog.tail) { @@ -601,6 +603,17 @@ static inline void sk_add_backlog(struct sock *sk, struct sk_buff *skb) skb->next = NULL; } +/* The per-socket spinlock must be held here. */ +static inline int sk_add_backlog_limited(struct sock *sk, struct sk_buff *skb) +{ + if (sk->sk_backlog.len >= max(sk->sk_backlog.limit, sk->sk_rcvbuf << 1)) + return -ENOBUFS; + + sk_add_backlog(sk, skb); + sk->sk_backlog.len += skb->truesize; + return 0; +} + static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb) { return sk->sk_backlog_rcv(sk, skb); diff --git a/net/core/sock.c b/net/core/sock.c index fcd397a..6e22dc9 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); @@ -1139,6 +1143,7 @@ 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); /* @@ -1542,6 +1547,12 @@ 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; } /** @@ -1874,6 +1885,7 @@ 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 v1.1