From: Ido Schimmel <idosch@nvidia.com> stable inclusion from stable-v6.6.120 commit 5979338c83012110ccd45cae6517591770bfe536 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13408 CVE: CVE-2025-71097 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit ac782f4e3bfcde145b8a7f8af31d9422d94d172a ] When a nexthop object is deleted, it is marked as dead and then fib_table_flush() is called to flush all the routes that are using the dead nexthop. The current logic in fib_table_flush() is to only flush error routes (e.g., blackhole) when it is called as part of network namespace dismantle (i.e., with flush_all=true). Therefore, error routes are not flushed when their nexthop object is deleted: # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip route add 198.51.100.1/32 nhid 1 # ip route add blackhole 198.51.100.2/32 nhid 1 # ip nexthop del id 1 # ip route show blackhole 198.51.100.2 nhid 1 dev dummy1 As such, they keep holding a reference on the nexthop object which in turn holds a reference on the nexthop device, resulting in a reference count leak: # ip link del dev dummy1 [ 70.516258] unregister_netdevice: waiting for dummy1 to become free. Usage count = 2 Fix by flushing error routes when their nexthop is marked as dead. IPv6 does not suffer from this problem. Fixes: 493ced1ac47c ("ipv4: Allow routes to use nexthop objects") Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Closes: https://lore.kernel.org/netdev/d943f806-4da6-4970-ac28-b9373b0e63ac@I-love.S... Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com Signed-off-by: Ido Schimmel <idosch@nvidia.com> Reviewed-by: David Ahern <dsahern@kernel.org> Link: https://patch.msgid.link/20251221144829.197694-1-idosch@nvidia.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Li Xiasong <lixiasong1@huawei.com> --- net/ipv4/fib_trie.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index fa54b36b241a..4d148d089232 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -2059,10 +2059,11 @@ int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all) continue; } - /* Do not flush error routes if network namespace is - * not being dismantled + /* When not flushing the entire table, skip error + * routes that are not marked for deletion. */ - if (!flush_all && fib_props[fa->fa_type].error) { + if (!flush_all && fib_props[fa->fa_type].error && + !(fi->fib_flags & RTNH_F_DEAD)) { slen = fa->fa_slen; continue; } -- 2.34.1