linux-kernel - Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to

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Message-ID: <CAHP4M8VjsZqncVKjaLqE0Hb0b5pia7qo6Vz0hHnBUcbJm1fNeg@mail.gmail.com>
Date:   Wed, 10 Nov 2021 15:02:52 +0530
From:   Ajay Garg <ajaygargnsit@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Pavel Skripkin <paskripkin@...il.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>, kernel@...il.dk,
        David Laight <David.Laight@...lab.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tty: vt: keyboard: do not copy an extra-byte in copy_to_user

> >
> > That's right Pavel.
> > Every function must work correctly as it "advertises", instead of
> > relying on "chancy correctness" of the calls leading to the method.
>
> That is not how the kernel works, sorry.  Otherwise every function would
> have to always verify all parameters passed to them, causing slow downs
> and redundant checks everywhere.
>

Hmm, agreed. Every cycle saved in the kernel is performance gained.

That's why, the RFC for strlscpy [1] makes all the more sense, as it
would save cpu cycles by removing the requirement to check the
return-value for overflows/underflows (including the "issue" I am
trying to address in this particular thread, and which actually lead
to the RFC for strlscpy].

P.S. :

I am not an egoistic person, who wants to get into unnecessary fights
just to upheld one's ego.
All I am trying is to suggest improvements, that

* make things faster.
* keeps code to as minimum as possible.
* makes developers' lives as comfortable as possible.

[1]
https://lore.kernel.org/linux-hardening/CAHP4M8WnLA0780yN+bpuuCtir+DLJRxe0atAiLbZO0bTGf6J-Q@mail.gmail.com/T/#m4a3f524eefe283a42430905fa4c0dfc2c37b2819

Thanks and Regards,
Ajay