[IPV4] fib: fix route replacement, fib_info is shared

fib_info can be shared by many route prefixes but we don't want
duplicate alternative routes for a prefix+tos+priority. Last change
was not correct to check fib_treeref because it accounts usage from
other prefixes. Additionally, avoid replacement without error if new
route is same, as Joonwoo Park suggests.

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

1 files changed, 31 insertions, 16 deletions

diff --git a/net/ipv4/fib_hash.c b/net/ipv4/fib_hash.c
index a15b2f1b2721..76b9c684cccd 100644
--- a/net/ipv4/fib_hash.c
+++ b/net/ipv4/fib_hash.c
@@ -424,19 +424,43 @@ static int fn_hash_insert(struct fib_table *tb, struct fib_config *cfg)
 
         if (fa && fa->fa_tos == tos &&
             fa->fa_info->fib_priority == fi->fib_priority) {
-                struct fib_alias *fa_orig;
+                struct fib_alias *fa_first, *fa_match;
 
                 err = -EEXIST;
                 if (cfg->fc_nlflags & NLM_F_EXCL)
                         goto out;
 
+                /* We have 2 goals:
+                 * 1. Find exact match for type, scope, fib_info to avoid
+                 * duplicate routes
+                 * 2. Find next 'fa' (or head), NLM_F_APPEND inserts before it
+                 */
+                fa_match = NULL;
+                fa_first = fa;
+                fa = list_entry(fa->fa_list.prev, struct fib_alias, fa_list);
+                list_for_each_entry_continue(fa, &f->fn_alias, fa_list) {
+                        if (fa->fa_tos != tos)
+                                break;
+                        if (fa->fa_info->fib_priority != fi->fib_priority)
+                                break;
+                        if (fa->fa_type == cfg->fc_type &&
+                            fa->fa_scope == cfg->fc_scope &&
+                            fa->fa_info == fi) {
+                                fa_match = fa;
+                                break;
+                        }
+                }
+
                 if (cfg->fc_nlflags & NLM_F_REPLACE) {
                         struct fib_info *fi_drop;
                         u8 state;
 
-                        if (fi->fib_treeref > 1)
+                        fa = fa_first;
+                        if (fa_match) {
+                                if (fa == fa_match)
+                                        err = 0;
                                 goto out;
-
+                        }
                         write_lock_bh(&fib_hash_lock);
                         fi_drop = fa->fa_info;
                         fa->fa_info = fi;
@@ -459,20 +483,11 @@ static int fn_hash_insert(struct fib_table *tb, struct fib_config *cfg)
                  * uses the same scope, type, and nexthop
                  * information.
                  */
-                fa_orig = fa;
-                fa = list_entry(fa->fa_list.prev, struct fib_alias, fa_list);
-                list_for_each_entry_continue(fa, &f->fn_alias, fa_list) {
-                        if (fa->fa_tos != tos)
-                                break;
-                        if (fa->fa_info->fib_priority != fi->fib_priority)
-                                break;
-                        if (fa->fa_type == cfg->fc_type &&
-                            fa->fa_scope == cfg->fc_scope &&
-                            fa->fa_info == fi)
-                                goto out;
-                }
+                if (fa_match)
+                        goto out;
+
                 if (!(cfg->fc_nlflags & NLM_F_APPEND))
-                        fa = fa_orig;
+                        fa = fa_first;
         }
 
         err = -ENOENT;