[IPVS]: Fix sched registration race when checking for name collision.

The register_ip_vs_scheduler() checks for the scheduler with the
same name under the read-locked __ip_vs_sched_lock, then drops,
takes it for writing and puts the scheduler in list.

This is racy, since we can have a race window between the lock
being re-locked for writing.

The fix is to search the scheduler with the given name right under
the write-locked __ip_vs_sched_lock.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ipvs/ip_vs_sched.c b/net/ipv4/ipvs/ip_vs_sched.c
index 1602304..4322358 100644 (file)
--- a/net/ipv4/ipvs/ip_vs_sched.c
+++ b/net/ipv4/ipvs/ip_vs_sched.c
@@ -183,19 +183,6 @@ int register_ip_vs_scheduler(struct ip_vs_scheduler *scheduler)
        /* increase the module use count */
        ip_vs_use_count_inc();
 
-       /*
-        *  Make sure that the scheduler with this name doesn't exist
-        *  in the scheduler list.
-        */
-       sched = ip_vs_sched_getbyname(scheduler->name);
-       if (sched) {
-               ip_vs_scheduler_put(sched);
-               ip_vs_use_count_dec();
-               IP_VS_ERR("register_ip_vs_scheduler(): [%s] scheduler "
-                         "already existed in the system\n", scheduler->name);
-               return -EINVAL;
-       }
-
        write_lock_bh(&__ip_vs_sched_lock);
 
        if (scheduler->n_list.next != &scheduler->n_list) {
@@ -207,6 +194,20 @@ int register_ip_vs_scheduler(struct ip_vs_scheduler *scheduler)
        }
 
        /*
+        *  Make sure that the scheduler with this name doesn't exist
+        *  in the scheduler list.
+        */
+       list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
+               if (strcmp(scheduler->name, sched->name) == 0) {
+                       write_unlock_bh(&__ip_vs_sched_lock);
+                       ip_vs_use_count_dec();
+                       IP_VS_ERR("register_ip_vs_scheduler(): [%s] scheduler "
+                                       "already existed in the system\n",
+                                       scheduler->name);
+                       return -EINVAL;
+               }
+       }
+       /*
         *      Add it into the d-linked scheduler list
         */
        list_add(&scheduler->n_list, &ip_vs_schedulers);