[PATCH] : bug fix in multipath drr code.

[pravin <pravins@xxxxxxxxxxxxxx>]

hi
 AFAIU, there is a race condition in multipath_drr code,
these code paths try to access & change last_selection variable
without any synchronization.

Please correct me if I am wrong.

Code Path - 1

__ip_route_output_key(...)
{
  ...
  calls drr_select_route
      if(FLOWI_FLAG_MULTIPATHOLDROUTE set){
          check last_selection.
          return  last_selection //so it can return NULL  pointer
      }
  ....
}

Code Path - 2  

rt_secret_rebuild()
{
.....
rt_run_flush(..);
     ->rt_free(rth);
             -> multipath_remove(rt)
                     ->drr_remove()
                             reset last_selection.
....
}

Attached patch also fixes bug in function drr_init ::
multipath_alg_register(..) is called with wrong algorithm ID.


Regards
Pravin.

Signed-off by: Pravin B. Shelar <pravins@xxxxxxxxxxxxxx>

Index: linux-2.6.12-rc4/net/ipv4/multipath_drr.c
===================================================================
--- linux-2.6.12-rc4.orig/net/ipv4/multipath_drr.c      2005-05-06 
22:20:31.000000000 -0700
+++ linux-2.6.12-rc4/net/ipv4/multipath_drr.c   2005-05-22 06:41:39.000000000 
-0700
@@ -145,11 +145,13 @@
        int cur_min_devidx = -1;
 
                /* if necessary and possible utilize the old alternative */
-       if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 &&
-           last_selection != NULL) {
-               result = last_selection;
-               *rp = result;
-               return;
+       if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 ) {
+               struct rtable *last_result = last_selection;
+               if(last_result != NULL &&
+                  multipath_comparekeys(&last_result->fl, flp)) {
+                       *rp = last_result;
+                       return;
+               }
        }
 
        /* 1. make sure all alt. nexthops have the same GC related data */
@@ -244,7 +246,7 @@
        if (err)
                return err;
 
-       err = multipath_alg_register(&drr_ops, IP_MP_ALG_RR);
+       err = multipath_alg_register(&drr_ops, IP_MP_ALG_DRR);
        if (err)
                goto fail;
 
Index: linux-2.6.12-rc4/net/ipv4/multipath_rr.c
===================================================================
--- linux-2.6.12-rc4.orig/net/ipv4/multipath_rr.c       2005-05-06 
22:20:31.000000000 -0700
+++ linux-2.6.12-rc4/net/ipv4/multipath_rr.c    2005-05-22 06:41:20.000000000 
-0700
@@ -64,10 +64,13 @@
        int min_use = -1;
 
        /* if necessary and possible utilize the old alternative */
-       if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 &&
-           last_used != NULL) {
-               result = last_used;
-               goto out;
+       if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 ) {
+               struct rtable *last_result = last_used;
+               if(last_result != NULL &&
+                  multipath_comparekeys(&last_result->fl, flp)) {
+                       result = last_result;
+                       goto out;
+               }
        }
 
        /* 1. make sure all alt. nexthops have the same GC related data