From be31fe6333f534155e6b408f1ef6d77974bb41aa Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Sun, 20 Sep 2026 19:14:32 +0000 Subject: [PATCH] ipv6: Fix dst leak for uncached routes. 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: 98aa546af5e4 ("inet: remove (struct uncached_list)->quarantine") Signed-off-by: Kuniyuki Iwashima Reviewed-by: Hangbin Liu Reviewed-by: Xuanqiang Luo Reviewed-by: Ido Schimmel Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260920191558.2990636-1-kuniyu@google.com Signed-off-by: Jakub Kicinski --- include/net/ip6_route.h | 4 ++-- net/ipv6/route.c | 7 ++++--- 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h index b9e8d2b759e9..0f9b7a260d25 100644 --- a/include/net/ip6_route.h +++ b/include/net/ip6_route.h @@ -101,12 +101,12 @@ static inline struct dst_entry *ip6_route_output(struct net *net, } /* Only conditionally release dst if flags indicates - * !RT6_LOOKUP_F_DST_NOREF or dst is in uncached_list. + * !RT6_LOOKUP_F_DST_NOREF or dst is uncached. */ 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 884d9ab0d50d..153ce16628c1 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -139,6 +139,7 @@ void rt6_uncached_list_add(struct rt6_info *rt) { struct uncached_list *ul = raw_cpu_ptr(&rt6_uncached_list); + /* Set once and never cleared: non-NULL marks an uncached route. */ rt->dst.rt_uncached_list = ul; spin_lock_bh(&ul->lock); @@ -2726,8 +2727,8 @@ struct dst_entry *ip6_route_output_flags(struct net *net, rcu_read_lock(); 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)) { + /* For an uncached dst, refcnt is already taken. */ + if (!rt6->dst.rt_uncached_list && !dst_hold_safe(dst)) { dst = &net->ipv6.ip6_null_entry->dst; dst_hold(dst); } @@ -2836,7 +2837,7 @@ 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);