netdev - Re: [PATCH] net: Avoid address overwrite in kernel

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Date: Mon, 21 Aug 2023 07:59:33 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <jrife@...gle.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>, <kuniyu@...zon.com>
Subject: Re: [PATCH] net: Avoid address overwrite in kernel_connect

From: Jordan Rife <jrife@...gle.com>
Date: Mon, 21 Aug 2023 05:00:06 -0500
> BPF programs that run on connect can rewrite the connect address. For
> the connect system call this isn't a problem, because a copy of the address
> is made when it is moved into kernel space. However, kernel_connect
> simply passes through the address it is given, so the caller may observe
> its address value unexpectedly change.
> 
> A practical example where this is problematic is where NFS is combined
> with a system such as Cilium which implements BPF-based load balancing.
> A common pattern in software-defined storage systems is to have an NFS
> mount that connects to a persistent virtual IP which in turn maps to an
> ephemeral server IP. This is usually done to achieve high availability:
> if your server goes down you can quickly spin up a replacement and remap
> the virtual IP to that endpoint. With BPF-based load balancing, mounts
> will forget the virtual IP address when the address rewrite occurs
> because a pointer to the only copy of that address is passed down the
> stack. Server failover then breaks, because clients have forgotten the
> virtual IP address. Reconnects fail and mounts remain broken. This patch
> was tested by setting up a scenario like this and ensuring that NFS
> reconnects worked after applying the patch.
> 
> Signed-off-by: Jordan Rife <jrife@...gle.com>
> ---
>  net/socket.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/socket.c b/net/socket.c
> index 2b0e54b2405c8..f49edb9b49185 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -3519,7 +3519,11 @@ EXPORT_SYMBOL(kernel_accept);
>  int kernel_connect(struct socket *sock, struct sockaddr *addr, int addrlen,
>  		   int flags)
>  {
> -	return sock->ops->connect(sock, addr, addrlen, flags);
> +	struct sockaddr_storage address;
> +
> +	memcpy(&address, addr, addrlen);
> +
> +	return sock->ops->connect(sock, (struct sockaddr *)&address, addrlen, flags);

Could you rebase on net-next.git ?  I think this patch conflicts with
1ded5e5a5931 ("net: annotate data-races around sock->ops").


>  }
>  EXPORT_SYMBOL(kernel_connect);
>  
> -- 
> 2.42.0.rc1.204.g551eb34607-goog