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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 27 Sep 2022 22:05:09 -0700
Message-ID: <CANn89iK1HHhvJgDsym377DDxZ3hvL8b8_pbrjb-qeXFRbsvFKA@mail.gmail.com>
Subject: Re: [PATCH v2 net 2/5] udp: Call inet6_destroy_sock() in setsockopt(IPV6_ADDRFORM).
To:     Kuniyuki Iwashima <kuniyu@amazon.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        David Ahern <dsahern@kernel.org>,
        Kuniyuki Iwashima <kuni1840@gmail.com>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Sep 27, 2022 at 5:28 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
>
> Commit 4b340ae20d0e ("IPv6: Complete IPV6_DONTFRAG support") forgot
> to add a change to free inet6_sk(sk)->rxpmtu while converting an IPv6
> socket into IPv4 with IPV6_ADDRFORM.  After conversion, sk_prot is
> changed to udp_prot and ->destroy() never cleans it up, resulting in
> a memory leak.
>
> This is due to the discrepancy between inet6_destroy_sock() and
> IPV6_ADDRFORM, so let's call inet6_destroy_sock() from IPV6_ADDRFORM
> to remove the difference.
>
> However, this is not enough for now because rxpmtu can be changed
> without lock_sock() after commit 03485f2adcde ("udpv6: Add lockless
> sendmsg() support").  We will fix this case in the following patch.
>
> Fixes: 4b340ae20d0e ("IPv6: Complete IPV6_DONTFRAG support")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  net/ipv6/ipv6_sockglue.c | 15 +++------------
>  1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index b61066ac8648..030a4cf23ceb 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -431,9 +431,6 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
>                 if (optlen < sizeof(int))
>                         goto e_inval;
>                 if (val == PF_INET) {
> -                       struct ipv6_txoptions *opt;
> -                       struct sk_buff *pktopt;
> -
>                         if (sk->sk_type == SOCK_RAW)
>                                 break;
>
> @@ -464,7 +461,6 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
>                                 break;
>                         }
>
> -                       fl6_free_socklist(sk);
>                         __ipv6_sock_mc_close(sk);
>                         __ipv6_sock_ac_close(sk);
>
> @@ -501,14 +497,9 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
>                                 sk->sk_socket->ops = &inet_dgram_ops;
>                                 sk->sk_family = PF_INET;
>                         }
> -                       opt = xchg((__force struct ipv6_txoptions **)&np->opt,
> -                                  NULL);
> -                       if (opt) {
> -                               atomic_sub(opt->tot_len, &sk->sk_omem_alloc);
> -                               txopt_put(opt);
> -                       }
> -                       pktopt = xchg(&np->pktoptions, NULL);
> -                       kfree_skb(pktopt);
> +

 Why is this needed ? I think a comment could help.
> +                       np->rxopt.all = 0;

> +                       inet6_destroy_sock(sk);

This name is unfortunate. This really is an inet6_cleanup_sock() in
this context.

>
>                         /*
>                          * ... and add it to the refcnt debug socks count
> --
> 2.30.2
>