ipvs: fix crash if scheduler is changed

I overlooked the svc->sched_data usage from schedulers
when the services were converted to RCU in 3.10. Now
the rare ipvsadm -E command can change the scheduler
but due to the reverse order of ip_vs_bind_scheduler
and ip_vs_unbind_scheduler we provide new sched_data
to the old scheduler resulting in a crash.

To fix it without changing the scheduler methods we
have to use synchronize_rcu() only for the editing case.
It means all svc->scheduler readers should expect a
NULL value. To avoid breakage for the service listing
and ipvsadm -R we can use the "none" name to indicate
that scheduler is not assigned, a state when we drop
new connections.

Reported-by: Alexander Vasiliev <a.vasylev@404-group.com>
Fixes: ceec4c381681 ("ipvs: convert services to rcu")
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

1 files changed, 6 insertions, 6 deletions

diff --git a/net/netfilter/ipvs/ip_vs_sched.c b/net/netfilter/ipvs/ip_vs_sched.c
index 199760c..7e81416 100644
--- a/net/netfilter/ipvs/ip_vs_sched.c
+++ b/net/netfilter/ipvs/ip_vs_sched.c
@@ -74,7 +74,7 @@ void ip_vs_unbind_scheduler(struct ip_vs_service *svc,
 
 	if (sched->done_service)
 		sched->done_service(svc);
-	/* svc->scheduler can not be set to NULL */
+	/* svc->scheduler can be set to NULL only by caller */
 }
 
 
@@ -147,21 +147,21 @@ void ip_vs_scheduler_put(struct ip_vs_scheduler *scheduler)
 
 void ip_vs_scheduler_err(struct ip_vs_service *svc, const char *msg)
 {
-	struct ip_vs_scheduler *sched;
+	struct ip_vs_scheduler *sched = rcu_dereference(svc->scheduler);
+	char *sched_name = sched ? sched->name : "none";
 
-	sched = rcu_dereference(svc->scheduler);
 	if (svc->fwmark) {
 		IP_VS_ERR_RL("%s: FWM %u 0x%08X - %s\n",
-			     sched->name, svc->fwmark, svc->fwmark, msg);
+			     sched_name, svc->fwmark, svc->fwmark, msg);
 #ifdef CONFIG_IP_VS_IPV6
 	} else if (svc->af == AF_INET6) {
 		IP_VS_ERR_RL("%s: %s [%pI6c]:%d - %s\n",
-			     sched->name, ip_vs_proto_name(svc->protocol),
+			     sched_name, ip_vs_proto_name(svc->protocol),
 			     &svc->addr.in6, ntohs(svc->port), msg);
 #endif
 	} else {
 		IP_VS_ERR_RL("%s: %s %pI4:%d - %s\n",
-			     sched->name, ip_vs_proto_name(svc->protocol),
+			     sched_name, ip_vs_proto_name(svc->protocol),
 			     &svc->addr.ip, ntohs(svc->port), msg);
 	}
 }