Re: [PATCH v5 net 2/5] udp: Call inet6_destroy_sock() in setsockopt(IPV6_ADDRFORM).

[Paolo Abeni <pabeni@redhat.com>]

On Thu, 2022-10-06 at 11:53 -0700, Kuniyuki Iwashima 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.
> 
> Note we will rename inet6_destroy_sock() to inet6_cleanup_sock() and
> remove unnecessary inet6_destroy_sock() calls in sk_prot->destroy()
> in the future.
> 
> Fixes: 4b340ae20d0e ("IPv6: Complete IPV6_DONTFRAG support")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
> Cc: Brian Haley <brian.haley@hp.com>
> ---
>  include/net/ipv6.h       |  1 +
>  net/ipv6/af_inet6.c      |  6 ++++++
>  net/ipv6/ipv6_sockglue.c | 20 ++++++++------------
>  3 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> index d664ba5812d8..335a49ecd8a0 100644
> --- a/include/net/ipv6.h
> +++ b/include/net/ipv6.h
> @@ -1182,6 +1182,7 @@ 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_cleanup_sock(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/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index d40b7d60e00e..ded827944fa6 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -510,6 +510,12 @@ void inet6_destroy_sock(struct sock *sk)
>  }
>  EXPORT_SYMBOL_GPL(inet6_destroy_sock);
>  
> +void inet6_cleanup_sock(struct sock *sk)
> +{
> +	inet6_destroy_sock(sk);
> +}
> +EXPORT_SYMBOL_GPL(inet6_cleanup_sock);
> +
>  /*
>   *	This does both peername and sockname.
>   */
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index 408345fc4c5c..a20edae868fd 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -431,9 +431,6 @@ 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 @@ 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 +497,14 @@ 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);
> +
> +			/* Disable all options not to allocate memory anymore,
> +			 * but there is still a race.  See the lockless path
> +			 * in udpv6_sendmsg() and ipv6_local_rxpmtu().
> +			 */
> +			np->rxopt.all = 0;
> +
> +			inet6_cleanup_sock(sk);

I think there still a pending point raised from Eric here. 

"""
Once the v6 socket has been transformed to IPv4 one,
inet6_sock_destruct() is not going to be called.
"""

AFAICS the series is safe Kuniyuki noted:

"""
inet6_sock_destruct() is set to sk->sk_destruct(), which is not changed
by the transformation and will be called from __sk_destruct().
"""
[with the next patch]

@Eric are you fine with the above?

Thanks!

Paolo


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