netdev - Re: [PATCH] net: check the return value of the copy_from

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Message-ID: <ZuH4B7STmaY0AI1m@mini-arch>
Date: Wed, 11 Sep 2024 13:05:27 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>,
	Qianqiang Liu <qianqiang.liu@....com>, davem@...emloft.net,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: check the return value of the copy_from_sockptr

On 09/11, Cong Wang wrote:
> On Wed, Sep 11, 2024 at 11:49:32AM -0700, Stanislav Fomichev wrote:
> > Can you explain what is not correct?
> > 
> > Calling BPF_CGROUP_RUN_PROG_GETSOCKOPT with max_optlen=0 should not be
> > a problem I think? (the buffer simply won't be accessible to the bpf prog)
> 
> Sure. Sorry for not providing all the details.
> 
> If I understand the behavior of copy_from_user() correctly, it may
> return partially copied data in case of error, which then leads to a
> partially-copied 'max_optlen'.
> 
> So, do you expect a partially-copied max_optlen to be passed to the
> eBPF program meanwhile the user still expects a complete one (since no
> -EFAULT)?
> 
> Thanks.

Partial copy is basically the same as user giving us garbage input, right?
That should still be handled correctly I think.

__cgroup_bpf_run_filter_getsockopt (via sockopt_alloc_buf) should handle both cases correctly:
- garbage input / partial copy resulting in negative number -> EINVAL
- garbage input / partial copy resulting in too large number -> potentially
  EFAULT when trying to copy PAGE_SIZE-worth of data

Also, for the EOPNOTSUPP case, we shouldn't even bother copying any data.

Am I missing something?