[IPV4]: Fix refcount damaging in net/ipv4/route.c

	One such place that can damage the dst refcnts is route.c with
CONFIG_IP_ROUTE_MULTIPATH_CACHED enabled, i don't see the user's
.config. In this new code i see that rt_intern_hash is called before
dst->refcnt is set to 1, dst is the 2nd arg to rt_intern_hash.

Arg 2 of rt_intern_hash must come with refcnt 1 as it is added to
table or dropped depending on error/add/update. One such example is
ip_mkroute_input where __mkroute_input return rth with refcnt 0 which
is provided to rt_intern_hash. ip_mkroute_output looks like a 2nd such
place. Appending untested patch for comments and review.  The idea is
to put previous reference as we are going to return next result/error.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 15 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8c0b14e3beec..8549f26e2495 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1760,6 +1760,7 @@ static inline int __mkroute_input(struct sk_buff *skb,
                 goto cleanup;
         }
 
+        atomic_set(&rth->u.dst.__refcnt, 1);
         rth->u.dst.flags= DST_HOST;
 #ifdef CONFIG_IP_ROUTE_MULTIPATH_CACHED
         if (res->fi->fib_nhs > 1)
@@ -1820,7 +1821,6 @@ static inline int ip_mkroute_input_def(struct sk_buff *skb,
         err = __mkroute_input(skb, res, in_dev, daddr, saddr, tos, &rth);
         if (err)
                 return err;
-        atomic_set(&rth->u.dst.__refcnt, 1);
 
         /* put it into the cache */
         hash = rt_hash_code(daddr, saddr ^ (fl->iif << 5), tos);
@@ -1834,8 +1834,8 @@ static inline int ip_mkroute_input(struct sk_buff *skb,
                                    u32 daddr, u32 saddr, u32 tos)
 {
 #ifdef CONFIG_IP_ROUTE_MULTIPATH_CACHED
-        struct rtable* rth = NULL;
-        unsigned char hop, hopcount, lasthop;
+        struct rtable* rth = NULL, *rtres;
+        unsigned char hop, hopcount;
         int err = -EINVAL;
         unsigned int hash;
 
@@ -1844,8 +1844,6 @@ static inline int ip_mkroute_input(struct sk_buff *skb,
         else
                 hopcount = 1;
 
-        lasthop = hopcount - 1;
-
         /* distinguish between multipath and singlepath */
         if (hopcount < 2)
                 return ip_mkroute_input_def(skb, res, fl, in_dev, daddr,
@@ -1855,6 +1853,10 @@ static inline int ip_mkroute_input(struct sk_buff *skb,
         for (hop = 0; hop < hopcount; hop++) {
                 res->nh_sel = hop;
 
+                /* put reference to previous result */
+                if (hop)
+                        ip_rt_put(rtres);
+
                 /* create a routing cache entry */
                 err = __mkroute_input(skb, res, in_dev, daddr, saddr, tos,
                                       &rth);
@@ -1863,7 +1865,7 @@ static inline int ip_mkroute_input(struct sk_buff *skb,
 
                 /* put it into the cache */
                 hash = rt_hash_code(daddr, saddr ^ (fl->iif << 5), tos);
-                err = rt_intern_hash(hash, rth, (struct rtable**)&skb->dst);
+                err = rt_intern_hash(hash, rth, &rtres);
                 if (err)
                         return err;
 
@@ -1873,13 +1875,8 @@ static inline int ip_mkroute_input(struct sk_buff *skb,
                                      FIB_RES_NETMASK(*res),
                                      res->prefixlen,
                                      &FIB_RES_NH(*res));
-
-                /* only for the last hop the reference count is handled
-                 * outside
-                 */
-                if (hop == lasthop)
-                        atomic_set(&(skb->dst->__refcnt), 1);
         }
+        skb->dst = &rtres->u.dst;
         return err;
 #else /* CONFIG_IP_ROUTE_MULTIPATH_CACHED  */
         return ip_mkroute_input_def(skb, res, fl, in_dev, daddr, saddr, tos);
@@ -2208,6 +2205,7 @@ static inline int __mkroute_output(struct rtable **result,
                 goto cleanup;
         }               
 
+        atomic_set(&rth->u.dst.__refcnt, 1);
         rth->u.dst.flags= DST_HOST;
 #ifdef CONFIG_IP_ROUTE_MULTIPATH_CACHED
         if (res->fi) {
@@ -2290,8 +2288,6 @@ static inline int ip_mkroute_output_def(struct rtable **rp,
         if (err == 0) {
                 u32 tos = RT_FL_TOS(oldflp);
 
-                atomic_set(&rth->u.dst.__refcnt, 1);
-                
                 hash = rt_hash_code(oldflp->fl4_dst, 
                                     oldflp->fl4_src ^ (oldflp->oif << 5), tos);
                 err = rt_intern_hash(hash, rth, rp);
@@ -2326,6 +2322,10 @@ static inline int ip_mkroute_output(struct rtable** rp,
                         dev2nexthop = FIB_RES_DEV(*res);
                         dev_hold(dev2nexthop);
 
+                        /* put reference to previous result */
+                        if (hop)
+                                ip_rt_put(*rp);
+
                         err = __mkroute_output(&rth, res, fl, oldflp,
                                                dev2nexthop, flags);
 
@@ -2350,7 +2350,6 @@ static inline int ip_mkroute_output(struct rtable** rp,
                         if (err != 0)
                                 return err;
                 }
-                atomic_set(&(*rp)->u.dst.__refcnt, 1);
                 return err;
         } else {
                 return ip_mkroute_output_def(rp, res, fl, oldflp, dev_out,