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authorJeff Layton <jlayton@redhat.com>2008-10-20 11:51:57 -0400
committerJ. Bruce Fields <bfields@citi.umich.edu>2009-01-06 11:53:47 -0500
commitc9233eb7b0b11ef176d4bf68da2ce85464b6ec39 (patch)
tree22f9f999e0d48a5f3aae6b32f9ff702eb4db05cc /net
parent548eaca46b3cf4419b6c2be839a106d8641ffb70 (diff)
downloadlinux-c9233eb7b0b11ef176d4bf68da2ce85464b6ec39.tar.gz
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 <jlayton@redhat.com> Acked-by: Neil Brown <neilb@suse.de> Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Diffstat (limited to 'net')
-rw-r--r--net/sunrpc/svc_xprt.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index bf5b5cdafeb..3fe4f100427 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,