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Message-ID: <20220928043121.79393-1-kuniyu@amazon.com>
Date: Tue, 27 Sep 2022 21:31:21 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <dsahern@...nel.org>, <kuba@...nel.org>,
<kuni1840@...il.com>, <kuniyu@...zon.com>,
<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH v2 net 3/5] tcp/udp: Call inet6_destroy_sock() in IPv6 sk->sk_destruct().
From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 27 Sep 2022 21:10:22 -0700
> On Tue, Sep 27, 2022 at 9:00 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > From: Eric Dumazet <edumazet@...gle.com>
> > Date: Tue, 27 Sep 2022 20:43:51 -0700
> > > On Tue, Sep 27, 2022 at 5:29 PM Kuniyuki Iwashima <kuniyu@...zon.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 IPv6 sk->sk_destruct() not to miss the future change and a similar
> > > > bug fixed in commit e27326009a3d ("net: ping6: Fix memleak in
> > > > ipv6_renew_options().")
> > >
> > > I do not see how your patches prevent rxpmtu to be created at the time
> > > of IPV6_ADDRFROM ?
> > >
> > > There seem to be races.
> > >
> > > lockless UDP sendmsg() is a disaster really.
> >
> > I think we are never able to prevent it and races exist unless we remove
> > the lockless path itself, so the patch makes sure to free rxpmtu at least
> > when we close() the socket. Currently, we can not even free it.
>
> I am saying your patches do not guarantee the rxpmtu is freed at close() time.
>
> Once the v6 socket has been transformed to IPv4 one,
> inet6_sock_destruct() is not going to be called.
inet6_sock_destruct() is set to sk->sk_destruct(), which is not changed
by the transformation and will be called from __sk_destruct().
But I might be missing something.
The lockless sendmsg() keeps sk_wmem_alloc > 0 after the conversion and
prevents sk_free() ?
> > > > We can now remove all inet6_destroy_sock() calls from IPv6 protocol
> > > > specific ->destroy() functions, but such changes are invasive to
> > > > backport. 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@...zon.com>
> > > > ---
> > > > include/net/ipv6.h | 1 +
> > > > include/net/udp.h | 2 +-
> > > > net/ipv4/udp.c | 8 ++++++--
> > > > net/ipv6/af_inet6.c | 9 ++++++++-
> > > > net/ipv6/udp.c | 15 ++++++++++++++-
> > > > 5 files changed, 30 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> > > > index de9dcc5652c4..11f1a9a8b066 100644
> > > > --- a/include/net/ipv6.h
> > > > +++ b/include/net/ipv6.h
> > > > @@ -1178,6 +1178,7 @@ void ipv6_icmp_error(struct sock *sk, struct sk_buff *skb, int err, __be16 port,
> > > > void ipv6_local_error(struct sock *sk, int err, struct flowi6 *fl6, u32 info);
> > > > void ipv6_local_rxpmtu(struct sock *sk, struct flowi6 *fl6, u32 mtu);
> > > >
> > > > +void inet6_sock_destruct(struct sock *sk);
> > > > int inet6_release(struct socket *sock);
> > > > int inet6_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len);
> > > > int inet6_getname(struct socket *sock, struct sockaddr *uaddr,
> > > > diff --git a/include/net/udp.h b/include/net/udp.h
> > > > index 5ee88ddf79c3..fee053bcd17c 100644
> > > > --- a/include/net/udp.h
> > > > +++ b/include/net/udp.h
> > > > @@ -247,7 +247,7 @@ static inline bool udp_sk_bound_dev_eq(struct net *net, int bound_dev_if,
> > > > }
> > > >
> > > > /* net/ipv4/udp.c */
> > > > -void udp_destruct_sock(struct sock *sk);
> > > > +void udp_destruct_common(struct sock *sk);
> > > > void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len);
> > > > int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb);
> > > > void udp_skb_destructor(struct sock *sk, struct sk_buff *skb);
> > > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > > > index 560d9eadeaa5..a84ae44db7e2 100644
> > > > --- a/net/ipv4/udp.c
> > > > +++ b/net/ipv4/udp.c
> > > > @@ -1598,7 +1598,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
> > > > }
> > > > EXPORT_SYMBOL_GPL(__udp_enqueue_schedule_skb);
> > > >
> > > > -void udp_destruct_sock(struct sock *sk)
> > > > +void udp_destruct_common(struct sock *sk)
> > > > {
> > > > /* reclaim completely the forward allocated memory */
> > > > struct udp_sock *up = udp_sk(sk);
> > > > @@ -1611,10 +1611,14 @@ void udp_destruct_sock(struct sock *sk)
> > > > kfree_skb(skb);
> > > > }
> > > > udp_rmem_release(sk, total, 0, true);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(udp_destruct_common);
> > > >
> > > > +static void udp_destruct_sock(struct sock *sk)
> > > > +{
> > > > + udp_destruct_common(sk);
> > > > inet_sock_destruct(sk);
> > > > }
> > > > -EXPORT_SYMBOL_GPL(udp_destruct_sock);
> > > >
> > > > int udp_init_sock(struct sock *sk)
> > > > {
> > > > diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> > > > index dbb1430d6cc2..0774cff62f2d 100644
> > > > --- a/net/ipv6/af_inet6.c
> > > > +++ b/net/ipv6/af_inet6.c
> > > > @@ -109,6 +109,13 @@ static __inline__ struct ipv6_pinfo *inet6_sk_generic(struct sock *sk)
> > > > return (struct ipv6_pinfo *)(((u8 *)sk) + offset);
> > > > }
> > > >
> > > > +void inet6_sock_destruct(struct sock *sk)
> > > > +{
> > > > + inet6_destroy_sock(sk);
> > > > + inet_sock_destruct(sk);
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(inet6_sock_destruct);
> > > > +
> > > > static int inet6_create(struct net *net, struct socket *sock, int protocol,
> > > > int kern)
> > > > {
> > > > @@ -201,7 +208,7 @@ static int inet6_create(struct net *net, struct socket *sock, int protocol,
> > > > inet->hdrincl = 1;
> > > > }
> > > >
> > > > - sk->sk_destruct = inet_sock_destruct;
> > > > + sk->sk_destruct = inet6_sock_destruct;
> > > > sk->sk_family = PF_INET6;
> > > > sk->sk_protocol = protocol;
> > > >
> > > > diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> > > > index 3366d6a77ff2..a5256f7184ab 100644
> > > > --- a/net/ipv6/udp.c
> > > > +++ b/net/ipv6/udp.c
> > > > @@ -56,6 +56,19 @@
> > > > #include <trace/events/skb.h>
> > > > #include "udp_impl.h"
> > > >
> > > > +static void udpv6_destruct_sock(struct sock *sk)
> > > > +{
> > > > + udp_destruct_common(sk);
> > > > + inet6_sock_destruct(sk);
> > > > +}
> > > > +
> > > > +static int udpv6_init_sock(struct sock *sk)
> > > > +{
> > > > + skb_queue_head_init(&udp_sk(sk)->reader_queue);
> > > > + sk->sk_destruct = udpv6_destruct_sock;
> > > > + return 0;
> > > > +}
> > > > +
> > > > static u32 udp6_ehashfn(const struct net *net,
> > > > const struct in6_addr *laddr,
> > > > const u16 lport,
> > > > @@ -1723,7 +1736,7 @@ struct proto udpv6_prot = {
> > > > .connect = ip6_datagram_connect,
> > > > .disconnect = udp_disconnect,
> > > > .ioctl = udp_ioctl,
> > > > - .init = udp_init_sock,
> > > > + .init = udpv6_init_sock,
> > > > .destroy = udpv6_destroy_sock,
> > > > .setsockopt = udpv6_setsockopt,
> > > > .getsockopt = udpv6_getsockopt,
> > > > --
> > > > 2.30.2
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