ipv6: fib6_rules should return exact return value

With the addition of the suppress operation
(7764a45a8f1fe74d4f7d301eaca2e558e7e2831a ("fib_rules: add .suppress
operation") we rely on accurate error reporting of the fib_rules.actions.

fib6_rule_action always returned -EAGAIN in case we could not find a
matching route and 0 if a rule was matched. This also included a match
for blackhole or prohibited rule actions which could get suppressed by
the new logic.

So adapt fib6_rule_action to always return the correct error code as
its counterpart fib4_rule_action does. This also fixes a possiblity of
nullptr-deref where we don't find a table, thus rt == NULL. Because
the condition rt != ip6_null_entry still holdes it seems we could later
get a nullptr bug on dereference rt->dst.

v2:
a) Fixed a brain fart in the commit msg (the rule => a table, etc). No
   changes to the patch.

Cc: Stefan Tomanek <stefan.tomanek@wertarbyte.de>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 3 deletions

diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
index e64e6a55fc4a..554a4fbabfb3 100644
--- a/net/ipv6/fib6_rules.c
+++ b/net/ipv6/fib6_rules.c
@@ -55,26 +55,33 @@ static int fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
         struct fib6_table *table;
         struct net *net = rule->fr_net;
         pol_lookup_t lookup = arg->lookup_ptr;
+        int err = 0;
 
         switch (rule->action) {
         case FR_ACT_TO_TBL:
                 break;
         case FR_ACT_UNREACHABLE:
+                err = -ENETUNREACH;
                 rt = net->ipv6.ip6_null_entry;
                 goto discard_pkt;
         default:
         case FR_ACT_BLACKHOLE:
+                err = -EINVAL;
                 rt = net->ipv6.ip6_blk_hole_entry;
                 goto discard_pkt;
         case FR_ACT_PROHIBIT:
+                err = -EACCES;
                 rt = net->ipv6.ip6_prohibit_entry;
                 goto discard_pkt;
         }
 
         table = fib6_get_table(net, rule->table);
-        if (table)
-                rt = lookup(net, table, flp6, flags);
+        if (!table) {
+                err = -EAGAIN;
+                goto out;
+        }
 
+        rt = lookup(net, table, flp6, flags);
         if (rt != net->ipv6.ip6_null_entry) {
                 struct fib6_rule *r = (struct fib6_rule *)rule;
 
@@ -101,6 +108,7 @@ static int fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
         }
 again:
         ip6_rt_put(rt);
+        err = -EAGAIN;
         rt = NULL;
         goto out;
 
@@ -108,7 +116,7 @@ discard_pkt:
         dst_hold(&rt->dst);
 out:
         arg->result = rt;
-        return rt == NULL ? -EAGAIN : 0;
+        return err;
 }
 
 static bool fib6_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg)