Re: [PATCH net v4 2/3] net: prevent rewrite of msg_name in sock_sendmsg()

[Paolo Abeni <pabeni@redhat.com>]

On Wed, 2023-09-20 at 09:28 -0400, Willem de Bruijn wrote:
> 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@vger.kernel.org
> > Signed-off-by: Jordan Rife <jrife@google.com>
> 
> Reviewed-by: Willem de Bruijn <willemb@google.com>

CC Jens and Pavel, as I guess io_uring likely want to use
__sock_sendmsg(), in a follow-up patch.

Cheers,

Paolo