[PATCH v1 net] ipv6: Fix dst leak for uncached routes.

[Kuniyuki Iwashima <kuniyu@google.com>]

ip6_route_output_flags(), ip6_rt_put_flags(), and ip6_dst_check()
detect an uncached route by list_empty(&rt->dst.rt_uncached),
which replaced the static DST_NOCACHE flag check in commit
a4c2fd7f7891 ("net: remove DST_NOCACHE flag").

When a device is unregistered, rt6_uncached_list_flush_dev()
unlinks uncached routes tied to the device from rt6_uncached_list.

Previously, they were moved to another list with list_move()
(__list_del_entry() + list_add()), and since commit 98aa546af5e4
("inet: remove (struct uncached_list)->quarantine"), the routes
are just unlinked with list_del_init().

If list_del_init() runs concurrently, list_empty() evaluates to
true; ip6_route_output_flags() calls dst_hold_safe() incorrectly
and ip6_rt_put_flags() skips ip6_rt_put(), leaking dst, and thus
dev tied via rt->from as well.

The same race is partially fixed by commit 9a6f0c4d5796 ("dst:
fix races in rt6_uncached_list_del() and rt_del_uncached_list()").

Let's check rt6->dst.rt_uncached_list instead.

Note that IPv4 does not have the same issue.

Fixes: 7d9e5f422150 ("ipv6: convert major tx path to use RT6_LOOKUP_F_DST_NOREF")
Fixes: d64a1f574a29 ("ipv6: honor RT6_LOOKUP_F_DST_NOREF in rule lookup logic")
Fixes: a4c2fd7f7891 ("net: remove DST_NOCACHE flag")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/ip6_route.h | 2 +-
 net/ipv6/route.c        | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index b9e8d2b759e9..2c5ded121f54 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -106,7 +106,7 @@ static inline struct dst_entry *ip6_route_output(struct net *net,
 static inline void ip6_rt_put_flags(struct rt6_info *rt, int flags)
 {
 	if (!(flags & RT6_LOOKUP_F_DST_NOREF) ||
-	    !list_empty(&rt->dst.rt_uncached))
+	    rt->dst.rt_uncached_list)
 		ip6_rt_put(rt);
 }
 
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 08bd68f1b5bb..b18cd0d9148c 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2722,7 +2722,7 @@ struct dst_entry *ip6_route_output_flags(struct net *net,
 	dst = ip6_route_output_flags_noref(net, sk, fl6, flags);
 	rt6 = dst_rt6_info(dst);
 	/* For dst cached in uncached_list, refcnt is already taken. */
-	if (list_empty(&rt6->dst.rt_uncached) && !dst_hold_safe(dst)) {
+	if (!rt6->dst.rt_uncached_list && !dst_hold_safe(dst)) {
 		dst = &net->ipv6.ip6_null_entry->dst;
 		dst_hold(dst);
 	}
@@ -2831,7 +2831,7 @@ INDIRECT_CALLABLE_SCOPE struct dst_entry *ip6_dst_check(struct dst_entry *dst,
 	from = rcu_dereference(rt->from);
 
 	if (from && (rt->rt6i_flags & RTF_PCPU ||
-	    unlikely(!list_empty(&rt->dst.rt_uncached))))
+	    unlikely(rt->dst.rt_uncached_list)))
 		dst_ret = rt6_dst_from_check(rt, from, cookie);
 	else
 		dst_ret = rt6_check(rt, from, cookie);
-- 
2.55.0.1082.g2b9226bbc0-goog