ipv6: fixes for RTF_CACHE entries

After the commit 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache"), the fib6 gc is not started after the creation of a RTF_CACHE via a redirect or pmtu update, since fib6_add() isn't invoked anymore for such dsts.

We need the fib6 gc to run periodically to clean the RTF_CACHE, or the dst will stay there forever.

Fix it by explicitly calling fib6_force_start_gc() on successful exception creation. gc_args->more accounting will ensure that the gc timer will run for whatever time needed to properly clean the table.

v2 -> v3:
- clarified the commit message

Fixes 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")

Signed-off-by Paolo Abeni <[email protected]>

---

 net/ipv6/route.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

net/ipv6/route.c +3 -2

index 01a103c23a6c..5c27313803d2 100644
@@ -1340,8 +1340,10 @@ static int rt6_insert_exception(struct rt6_info *nrt,
        spin_unlock_bh(&rt6_exception_lock);
 
        /* Update fn->fn_sernum to invalidate all cached dst */
-       if (!err)
+       if (!err) {
                fib6_update_sernum(ort);
+               fib6_force_start_gc(net);
+       }
 
        return err;
 }
--

2.13.6

After the commit 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache"), the fib6 gc is not started after the creation of a RTF_CACHE via a redirect or pmtu update, since fib6_add() isn't invoked anymore for such dsts.

We need the fib6 gc to run periodically to clean the RTF_CACHE, or the dst will stay there forever.

Fix it by explicitly calling fib6_force_start_gc() on successful exception creation. gc_args->more accounting will ensure that the gc timer will run for whatever time needed to properly clean the table.

v2 -> v3:
- clarified the commit message

Fixes 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")

Signed-off-by Paolo Abeni <[email protected]>

The commit 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache") partially reverted the commit 1e2ea8ad37be ("ipv6: set dst.obsolete when a cached route has expired").

As a result, RTF_CACHE dst referenced outside the fib tree will not be removed until the next sernum change; dst_check() does not fail on aged-out dst, and dst->__refcnt can't decrease: the aged out dst will stay valid for a potentially unlimited time after the timeout expiration.

This change explicitly removes RTF_CACHE dst from the fib tree when aged out. The rt6_remove_exception() logic will then obsolete the dst and other entities will drop the related reference on next dst_check().

pMTU exceptions are not aged-out, and are removed from the exception table only when the - usually considerably longer - ip6_rt_mtu_expires timeout expires.

v1 -> v2:
- do not touch dst.obsolete in rt6_remove_exception(), not needed
v2 -> v3:
- take care of pMTU exceptions, too

Fixes 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")

Signed-off-by Paolo Abeni <[email protected]>

---

 net/ipv6/route.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

net/ipv6/route.c +11 -2

index 5c27313803d2..87a15cbd0e8b 100644
@@ -1575,7 +1575,13 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
 {
        struct rt6_info *rt = rt6_ex->rt6i;
 
-       if (atomic_read(&rt->dst.__refcnt) == 1 &&
+       /* we are pruning and obsoleting aged-out and non gateway exceptions
+        * even if others have still references to them, so that on next
+        * dst_check() such references can be dropped.
+        * EXPIRES exceptions - e.g. pmtu-generated ones are pruned when
+        * expired, independently from their aging, as per RFC 8201 section 4
+        */
+       if (!(rt->rt6i_flags & RTF_EXPIRES) &&
            time_after_eq(now, rt->dst.lastuse + gc_args->timeout)) {
                RT6_TRACE("aging clone %p\n", rt);
                rt6_remove_exception(bucket, rt6_ex);

@@ -1595,6 +1601,10 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
                        rt6_remove_exception(bucket, rt6_ex);
                        return;
                }
+       } else if (__rt6_check_expired(rt)) {
+               RT6_TRACE("purging expired route %p\n", rt);
+               rt6_remove_exception(bucket, rt6_ex);
+               return;
        }
        gc_args->more++;
 }
--

2.13.6

The commit 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache") partially reverted the commit 1e2ea8ad37be ("ipv6: set dst.obsolete when a cached route has expired").

As a result, RTF_CACHE dst referenced outside the fib tree will not be removed until the next sernum change; dst_check() does not fail on aged-out dst, and dst->__refcnt can't decrease: the aged out dst will stay valid for a potentially unlimited time after the timeout expiration.

This change explicitly removes RTF_CACHE dst from the fib tree when aged out. The rt6_remove_exception() logic will then obsolete the dst and other entities will drop the related reference on next dst_check().

pMTU exceptions are not aged-out, and are removed from the exception table only when the - usually considerably longer - ip6_rt_mtu_expires timeout expires.

v1 -> v2:
- do not touch dst.obsolete in rt6_remove_exception(), not needed
v2 -> v3:
- take care of pMTU exceptions, too

Fixes 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")

Signed-off-by Paolo Abeni <[email protected]>

This series addresses 2 different but related issues with RTF_CACHE introduced by the recent refactory.

patch 1 restore the gc timer for such routes
patch 2 removes the aged out dst from the fib tree, properly coping with pMTU routes

v1 -> v2:
- dropped the for ip route show cache
- avoid touching dst.obsolete when the dst is aged out

v2 -> v3:
- take care of pMTU exceptions