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

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>
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Reviewed-by: Xuanqiang Luo <redacted>

Thanks,
Xuanqiang