Patchwork [V2,1/7] net: add limit for socket backlog

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Submitter Zhu Yi
Date March 3, 2010, 8:36 a.m.
Message ID <1267605389-7369-1-git-send-email-yi.zhu@intel.com>
Download mbox | patch
Permalink /patch/46774/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Zhu Yi - March 3, 2010, 8:36 a.m.
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 <alex.shi@intel.com>
Cc: David Miller <davem@davemloft.net>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru
Cc: "Pekka Savola (ipv6)" <pekkas@netcore.fi>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Vlad Yasevich <vladislav.yasevich@hp.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Cc: Jon Maloy <jon.maloy@ericsson.com>
Cc: Allan Stephens <allan.stephens@windriver.com>
Cc: Andrew Hendry <andrew.hendry@gmail.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 include/net/sock.h |   15 ++++++++++++++-
 net/core/sock.c    |   16 ++++++++++++++--
 2 files changed, 28 insertions(+), 3 deletions(-)
David Miller - March 3, 2010, 8:54 a.m.
Please don't selectively CC: me only on some of the patches
in a series that's meant to go into the networking tree.

I handle patch submissions by deleting the copies from my inbox that
come to me through the mailing list, so if you don't CC: me on all
of them I'll lose some of them.

Thanks.

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Zhu Yi - March 3, 2010, 9:01 a.m.
On Wed, 2010-03-03 at 16:54 +0800, David Miller wrote:
> 
> Please don't selectively CC: me only on some of the patches
> in a series that's meant to go into the networking tree.
> 
> I handle patch submissions by deleting the copies from my inbox that
> come to me through the mailing list, so if you don't CC: me on all
> of them I'll lose some of them. 

OK. The series is not final. I'll do so next time.

Thanks,
-yi

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Patch

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);