netdev - Re: [PATCH net v4 2/3] net: prevent rewrite of msg_name in sock

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Date: Wed, 20 Sep 2023 09:28:52 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jordan Rife <jrife@...gle.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 willemdebruijn.kernel@...il.com, 
 netdev@...r.kernel.org
Cc: dborkman@...nel.org, 
 Jordan Rife <jrife@...gle.com>, 
 stable@...r.kernel.org
Subject: Re: [PATCH net v4 2/3] net: prevent rewrite of msg_name in
 sock_sendmsg()

Jordan Rife wrote:
> Callers of sock_sendmsg(), and similarly kernel_sendmsg(), in kernel
> space may observe their value of msg_name change in cases where BPF
> sendmsg hooks rewrite the send address. This has been confirmed to break
> NFS mounts running in UDP mode and has the potential to break other
> systems.
> 
> This patch:
> 
> 1) Creates a new function called __sock_sendmsg() with same logic as the
>    old sock_sendmsg() function.
> 2) Replaces calls to sock_sendmsg() made by __sys_sendto() and
>    __sys_sendmsg() with __sock_sendmsg() to avoid an unnecessary copy,
>    as these system calls are already protected.
> 3) Modifies sock_sendmsg() so that it makes a copy of msg_name if
>    present before passing it down the stack to insulate callers from
>    changes to the send address.
> 
> Link: https://lore.kernel.org/netdev/20230912013332.2048422-1-jrife@google.com/
> Fixes: 1cedee13d25a ("bpf: Hooks for sys_sendmsg")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jordan Rife <jrife@...gle.com>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>