linux-kernel - RE: Writing to a const pointer: is this supposed to happen?

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Message-ID: <32182d4126fd49dabac4091b7a6c89e7@AcuMS.aculab.com>
Date:   Thu, 2 Jul 2020 07:55:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kars Mulder' <kerneldev@...smulder.nl>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pavel Machek <pavel@....cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>
Subject: RE: Writing to a const pointer: is this  supposed to happen?

From: Kars Mulder
> Sent: 02 July 2020 00:03
> On Saturday, June 27, 2020 12:24 CEST, David Laight wrote:
> > The code quoted (using strset()) is almost certainly wrong.
> > The caller is unlikely to expect the input be modified.
> > Since it doesn't fault the string must be in read-write memory.
> 
> I tried writing a patch that avoids the writing-to-const-pointer issue
> by using the less intrusive sscanf function instead of strsep. It might
> avoid a potential bug when somebody wrongly assumes that a
> kernel_param_ops.set function will not write to its const char* argument.

Hmm... sscanf() is also horrid.
Surprisingly difficult to use correctly.

It is usually best to use strchr() (and maybe str[c]scn())
to parse strings.
For numbers use whatever the kernels current 'favourite' implementation
of strtoul() is called.

	David

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