linux-kernel - RE: [PATCH 5.15.y] tty: add the option to have a tty reject a new ldisc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID:
 <IA1PR11MB61702B6E5E5031139DA5967BBB91A@IA1PR11MB6170.namprd11.prod.outlook.com>
Date: Wed, 14 May 2025 01:59:01 +0000
From: "Ren, Jianqi (Jacky) (CN)" <Jianqi.Ren.CN@...driver.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "penguin-kernel@...ove.sakura.ne.jp" <penguin-kernel@...ove.sakura.ne.jp>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "daniel.starke@...mens.com" <daniel.starke@...mens.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: RE: [PATCH 5.15.y] tty: add the option to have a tty reject a new
 ldisc

Hello,

We don't have such device, but we saw in the commit log that "use it to limit the virtual terminals to just N_TTY.  They are kind of special" and thought that it may help prevent other unexpected ldisc. So, we submitted this patch for review. If it's improper we will stop here for both 5.15 and 5.10.

-----Original Message-----
From: Greg KH <gregkh@...uxfoundation.org> 
Sent: Monday, May 12, 2025 22:10
To: Ren, Jianqi (Jacky) (CN) <Jianqi.Ren.CN@...driver.com>
Cc: stable@...r.kernel.org; patches@...ts.linux.dev; linux-kernel@...r.kernel.org; penguin-kernel@...ove.sakura.ne.jp; akpm@...ux-foundation.org; daniel.starke@...mens.com; torvalds@...ux-foundation.org
Subject: Re: [PATCH 5.15.y] tty: add the option to have a tty reject a new ldisc

CAUTION: This email comes from a non Wind River email account!
Do not click links or open attachments unless you recognize the sender and know the content is safe.

On Fri, May 09, 2025 at 05:14:54PM +0800, jianqi.ren.cn@...driver.com wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
>
> [ Upstream commit 6bd23e0c2bb6c65d4f5754d1456bc9a4427fc59b ]
>
> ... and use it to limit the virtual terminals to just N_TTY.  They are 
> kind of special, and in particular, the "con_write()" routine violates 
> the "writes cannot sleep" rule that some ldiscs rely on.
>
> This avoids the
>
>    BUG: sleeping function called from invalid context at 
> kernel/printk/printk.c:2659
>
> when N_GSM has been attached to a virtual console, and gsmld_write() 
> calls con_write() while holding a spinlock, and con_write() then tries 
> to get the console lock.

WHy do you want this in 5.15 and older kernels?  You have already disabledf n_gsm from your kernels already so this isn't an issue, right?
Unless you have this hardware, and explicitly know what is talking to it, that is the recommendation for this code.

And how was this and the 5.10.y backport tested?  Did you see the above "BUG:" line without it?

thanks,

greg k-h