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

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Message-ID: <ZuTdhIZtw8Hc7LXP@pop-os.localdomain>
Date: Fri, 13 Sep 2024 17:49:08 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Stanislav Fomichev <stfomichev@...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 Wed, Sep 11, 2024 at 01:05:27PM -0700, Stanislav Fomichev wrote:
> 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.

Not to me.

For explict garbage input, users (mostly syzbot) already expect it is a
garbage.

For partial copy, users expect either an error (like EFAULT) or a success
with the _original_ value.

It is all about expectation of the API.

Thanks.