From c9233eb7b0b11ef176d4bf68da2ce85464b6ec39 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Mon, 20 Oct 2008 11:51:57 -0400 Subject: sunrpc: add sv_maxconn field to svc_serv (try #3) svc_check_conn_limits() attempts to prevent denial of service attacks by having the service close old connections once it reaches a threshold. This threshold is based on the number of threads in the service: (serv->sv_nrthreads + 3) * 20 Once we reach this, we drop the oldest connections and a printk pops to warn the admin that they should increase the number of threads. Increasing the number of threads isn't an option however for services like lockd. We don't want to eliminate this check entirely for such services but we need some way to increase this limit. This patch adds a sv_maxconn field to the svc_serv struct. When it's set to 0, we use the current method to calculate the max number of connections. RPC services can then set this on an as-needed basis. Signed-off-by: Jeff Layton Acked-by: Neil Brown Signed-off-by: J. Bruce Fields --- net/sunrpc/svc_xprt.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) (limited to 'net/sunrpc/svc_xprt.c') diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index bf5b5cd..3fe4f10 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -515,8 +515,10 @@ int svc_port_is_privileged(struct sockaddr *sin) } /* - * Make sure that we don't have too many active connections. If we - * have, something must be dropped. + * Make sure that we don't have too many active connections. If we have, + * something must be dropped. It's not clear what will happen if we allow + * "too many" connections, but when dealing with network-facing software, + * we have to code defensively. Here we do that by imposing hard limits. * * There's no point in trying to do random drop here for DoS * prevention. The NFS clients does 1 reconnect in 15 seconds. An @@ -525,19 +527,27 @@ int svc_port_is_privileged(struct sockaddr *sin) * The only somewhat efficient mechanism would be if drop old * connections from the same IP first. But right now we don't even * record the client IP in svc_sock. + * + * single-threaded services that expect a lot of clients will probably + * need to set sv_maxconn to override the default value which is based + * on the number of threads */ static void svc_check_conn_limits(struct svc_serv *serv) { - if (serv->sv_tmpcnt > (serv->sv_nrthreads+3)*20) { + unsigned int limit = serv->sv_maxconn ? serv->sv_maxconn : + (serv->sv_nrthreads+3) * 20; + + if (serv->sv_tmpcnt > limit) { struct svc_xprt *xprt = NULL; spin_lock_bh(&serv->sv_lock); if (!list_empty(&serv->sv_tempsocks)) { if (net_ratelimit()) { /* Try to help the admin */ printk(KERN_NOTICE "%s: too many open " - "connections, consider increasing the " - "number of nfsd threads\n", - serv->sv_name); + "connections, consider increasing %s\n", + serv->sv_name, serv->sv_maxconn ? + "the max number of connections." : + "the number of threads."); } /* * Always select the oldest connection. It's not fair, -- cgit v1.1