linux-kernel - Re: [PATCH stable v2 1/2] arch/alpha, termios: implement BOTHER, IBSHIFT and termios2

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Message-ID: <20181008153840.GD3332@localhost>
Date:   Mon, 8 Oct 2018 17:38:40 +0200
From:   Johan Hovold <johan@...nel.org>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org,
        Tobias Klausmann <klausman@...warzvogel.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        linux-alpha@...r.kernel.org, linux-serial@...r.kernel.org,
        Johan Hovold <johan@...nel.org>,
        Alan Cox <alan@...rguk.ukuu.org.uk>, stable@...r.kernel.org
Subject: Re: [PATCH stable v2 1/2] arch/alpha, termios: implement BOTHER,
 IBSHIFT and termios2

On Sun, Oct 07, 2018 at 09:06:19PM -0700, H. Peter Anvin wrote:
> From: "H. Peter Anvin (Intel)" <hpa@...or.com>
> 
> Alpha has had c_ispeed and c_ospeed, but still set speeds in c_cflags
> using arbitrary flags. Because BOTHER is not defined, the general
> Linux code doesn't allow setting arbitrary baud rates, and because
> CBAUDEX == 0, we can have an array overrun of the baud_rate[] table in
> drivers/tty/tty_baudrate.c if (c_cflags & CBAUD) == 037.
> 
> Resolve both problems by #defining BOTHER to 037 on Alpha.
> 
> However, userspace still needs to know if setting BOTHER is actually
> safe given legacy kernels (does anyone actually care about that on
> Alpha anymore?), so enable the TCGETS2/TCSETS*2 ioctls on Alpha, even
> though they use the same structure. Define struct termios2 just for
> compatibility; it is the exact same structure as struct termios. In a
> future patchset, this will be cleaned up so the uapi headers are
> usable from libc.

Is this really needed? By defining BOTHER (and IBSHIFT which you forgot
to mention here) you are enabling arbitrary rates also through TCSETS on
alpha, right?

Johan