[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>

1 files changed, 14 insertions, 13 deletions

diff --git a/net/ipv4/ipvs/ip_vs_sched.c b/net/ipv4/ipvs/ip_vs_sched.c
index 1602304abbf9..432235861908 100644
--- 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);