Re: [PATCH v1 net 3/5] tcp/udp: Call inet6_destroy_sock() in IPv4 sk_prot->destroy().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 27 Sep 2022 09:50:04 -0700
> On Tue, Sep 27, 2022 at 9:13 AM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> >
> > Originally, inet6_sk(sk)->XXX were changed under lock_sock(), so we were
> > able to clean them up by calling inet6_destroy_sock() during the IPv6 ->
> > IPv4 conversion by IPV6_ADDRFORM.  However, commit 03485f2adcde ("udpv6:
> > Add lockless sendmsg() support") added a lockless memory allocation path,
> > which could cause a memory leak:
> >
> > setsockopt(IPV6_ADDRFORM)                 sendmsg()
> > +-----------------------+                 +-------+
> > - do_ipv6_setsockopt(sk, ...)             - udpv6_sendmsg(sk, ...)
> >   - lock_sock(sk)                           ^._ called via udpv6_prot
> >   - WRITE_ONCE(sk->sk_prot, &tcp_prot)          before WRITE_ONCE()
> >   - inet6_destroy_sock()
> >   - release_sock(sk)                        - ip6_make_skb(sk, ...)
> >                                               ^._ lockless fast path for
> >                                                   the non-corking case
> >
> >                                               - __ip6_append_data(sk, ...)
> >                                                 - ipv6_local_rxpmtu(sk, ...)
> >                                                   - xchg(&np->rxpmtu, skb)
> >                                                     ^._ rxpmtu is never freed.
> >
> >                                             - lock_sock(sk)
> >
> > For now, rxpmtu is only the case, but let's call inet6_destroy_sock()
> > in both TCP/UDP v4 destroy functions not to miss the future change.
> >
> > We can consolidate TCP/UDP v4/v6 destroy functions, but such changes
> > are too invasive to backport to stable.  So, they can be posted as a
> > follow-up later for net-next.
> >
> > Fixes: 03485f2adcde ("udpv6: Add lockless sendmsg() support")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> > Cc: Vladislav Yasevich <vyasevic@redhat.com>
> > ---
> >  net/ipv4/tcp_ipv4.c | 5 +++++
> >  net/ipv4/udp.c      | 6 ++++++
> >  net/ipv6/tcp_ipv6.c | 1 -
> >  3 files changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > index 5b019ba2b9d2..035b6c52a243 100644
> > --- a/net/ipv4/tcp_ipv4.c
> > +++ b/net/ipv4/tcp_ipv4.c
> > @@ -2263,6 +2263,11 @@ void tcp_v4_destroy_sock(struct sock *sk)
> >         tcp_saved_syn_free(tp);
> >
> >         sk_sockets_allocated_dec(sk);
> > +
> > +#if IS_ENABLED(CONFIG_IPV6)
> > +       if (sk->sk_prot_creator == &tcpv6_prot)
> > +               inet6_destroy_sock(sk);
> > +#endif
> >  }
> 
> This is ugly, and will not compile with CONFIG_IPV6=m, right ?

Ah, exactly...

ld: net/ipv4/tcp_ipv4.o: in function `tcp_v4_destroy_sock':
/mnt/ec2-user/kernel/214_tcp_ipv6_renew_options_memleak/net/ipv4/tcp_ipv4.c:2290: undefined reference to `tcpv6_prot'
ld: /mnt/ec2-user/kernel/214_tcp_ipv6_renew_options_memleak/net/ipv4/tcp_ipv4.c:2291: undefined reference to `inet6_destroy_sock'
ld: net/ipv4/udp.o: in function `udp_destroy_sock':
/mnt/ec2-user/kernel/214_tcp_ipv6_renew_options_memleak/net/ipv4/udp.c:2660: undefined reference to `udpv6_prot'
ld: /mnt/ec2-user/kernel/214_tcp_ipv6_renew_options_memleak/net/ipv4/udp.c:2661: undefined reference to `inet6_destroy_sock'

So, do we have to move these 4 under net/ipv4/ with #ifdef CONFIG_IPv6 ?


> >  EXPORT_SYMBOL(tcp_v4_destroy_sock);
> >
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 560d9eadeaa5..cdf131c0a819 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -115,6 +115,7 @@
> >  #include <net/udp_tunnel.h>
> >  #if IS_ENABLED(CONFIG_IPV6)
> >  #include <net/ipv6_stubs.h>
> > +#include <net/transp_v6.h>
> >  #endif
> >
> >  struct udp_table udp_table __read_mostly;
> > @@ -2666,6 +2667,11 @@ void udp_destroy_sock(struct sock *sk)
> >                 if (up->encap_enabled)
> >                         static_branch_dec(&udp_encap_needed_key);
> >         }
> > +
> > +#if IS_ENABLED(CONFIG_IPV6)
> > +       if (sk->sk_prot_creator == &udpv6_prot)
> > +               inet6_destroy_sock(sk);
> > +#endif
> >  }
> >
> >  /*
> > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > index e54eee80ce5f..1ff6a92f7774 100644
> > --- a/net/ipv6/tcp_ipv6.c
> > +++ b/net/ipv6/tcp_ipv6.c
> > @@ -1945,7 +1945,6 @@ static int tcp_v6_init_sock(struct sock *sk)
> >  static void tcp_v6_destroy_sock(struct sock *sk)
> >  {
> >         tcp_v4_destroy_sock(sk);
> > -       inet6_destroy_sock(sk);
> >  }
> >
> >  #ifdef CONFIG_PROC_FS
> > --
> > 2.30.2
> >