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

[Xuanqiang Luo <xuanqiang.luo@linux.dev>]

在 2026/9/18 12:14, Kuniyuki Iwashima 写道:
> 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>
> ---

Reviewed-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>

Thanks,
Xuanqiang