netdev - Re: [PATCH 2/2 net] sctp: fix an error code in sctp_sf_eat

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Message-ID: <CADvbK_e2JwH3OqFSu89EvrtGbBbuCvD-C=Db_sExjvD1EcVLrw@mail.gmail.com>
Date: Fri, 9 Jun 2023 19:04:17 -0400
From: Xin Long <lucien.xin@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Vlad Yasevich <vladislav.yasevich@...com>, 
	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	linux-sctp@...r.kernel.org, netdev@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/2 net] sctp: fix an error code in sctp_sf_eat_auth()

On Fri, Jun 9, 2023 at 12:41 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> On Fri, Jun 09, 2023 at 11:13:03AM -0400, Xin Long wrote:
> > This one looks good to me.
> >
> > But for the patch 1/2 (somehow it doesn't show up in my mailbox):
> >
> >   default:
> >   pr_err("impossible disposition %d in state %d, event_type %d, event_id %d\n",
> >         status, state, event_type, subtype.chunk);
> > - BUG();
> > + error = status;
> > + if (error >= 0)
> > + error = -EINVAL;
> > + WARN_ON_ONCE(1);
> >
> > I think from the sctp_do_sm() perspective, it expects the state_fn
> > status only from
> > enum sctp_disposition. It is a BUG to receive any other values and
> > must be fixed,
> > as you did in 2/2. It does the same thing as other functions in SCTP code, like
> > sctp_sf_eat_data_*(), sctp_retransmit() etc.
>
> It is a bug, sure.  And after my patch is applied it will still trigger
> a stack trace.  But we should only call the actual BUG() function
> in order to prevent filesystem corruption or a privilege escalation or
> something along those lines.
Hi, Dan,

Sorry, I'm not sure about this.

Look at the places where it's using  BUG(), it's not exactly the case, like
in ping_err() or ping_common_sendmsg(), BUG() are used more for
unexpected cases, which don't cause any filesystem corruption or a
privilege escalation.

You may also check more others under net/*.

>
> Calling BUG() makes the system unusable so it makes bugs harder to
> debug.  This is even mentioned in checkpatch.pl "Do not crash the kernel
> unless it is absolutely unavoidable--use WARN_ON_ONCE() plus recovery
> code (if feasible) instead of BUG() or variants".
>
"absolutely unavoidable", I think in a module, if it gets a case that is not
expected at all, and the consequence (it may cause or has caused) is
unsure, WARN_ON_ONCE() is not enough.

Thanks.