On Thu, Mar 7, 2024 at 12:05 AM Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> wrote:
>
> Commit 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in
> inet_twsk_purge()") added changes in inet_twsk_purge() to purge
> reqsk in per-netns ehash during netns dismantle.
>
> inet_csk_reqsk_queue_drop_and_put() will remove reqsk from per-netns
> ehash, but the iteration uses sk_nulls_for_each_rcu(), which is not
> safe.
>
> After removing reqsk, we need to restart iteration.
>
> Note that we need not check net->ns.count here because per-netns
> ehash does not have reqsk in other live netns. We will check
> net->ns.count in the following patch.
>
> Fixes: 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in inet_twsk_purge()")
> Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> ---
> net/ipv4/inet_timewait_sock.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
> index 5befa4de5b24..00cbebaa2c68 100644
> --- a/net/ipv4/inet_timewait_sock.c
> +++ b/net/ipv4/inet_timewait_sock.c
> @@ -287,6 +287,8 @@ void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
> struct request_sock *req = inet_reqsk(sk);
>
> inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
> +
> + goto restart;
> }
>
> continue;
Note how the RCU rules that I followed for TCP_TIME_WAIT made
me to grab a reference on tw->tw_refcnt, using refcount_inc_not_zero()
I think your code had multiple bugs, because
inet_csk_reqsk_queue_drop_and_put() could cause UAF
if the timer already fired and refcount went to zero already.
We also could add sk_nulls_for_each_rcu_safe() to avoid these pesky
"goto restart;"
