netdev - Re: [PATCH] IB/mlx5: add checking for "vf" from do

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Date:   Wed, 24 Apr 2019 11:24:26 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Parav Pandit <parav@...lanox.com>, netdev@...r.kernel.org,
        Leon Romanovsky <leon@...nel.org>,
        Eli Cohen <eli@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] IB/mlx5: add checking for "vf" from do_setvfinfo()

On Wed, Apr 24, 2019 at 05:08:20PM +0300, Dan Carpenter wrote:
> I think I'm just going to ask netdev for an opinion on this.  It could
> be that we're just reading the code wrong...

I don't think you are reading it wrong.

Allowing the compiler to implicitly cast a user controlled u32 to an
int is simply wrong in all cases, IMHO. 

If the value was intended to be signed from the user it should have
been a s32. Allowing an unsigned value to become interpreted as
negative so often leads to security bugs.

IMHO it would be a good thing for smatch to warn on the general case
of implicit casting of user controlled data to a smaller range
type. Particularly it can do a bounds analysis to show the control
flow hasn't somehow restricted the bounds to be compatible.

I've seen more that a few real world security bugs that are caused by
wrong use of 'int' like this :(

Jason