linux-kernel - Re: CVE-2021-47326: x86/signal: Detect and prevent an alternate signal stack overflow

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Date: Thu, 23 May 2024 15:31:03 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: cve@...nel.org, linux-kernel@...r.kernel.org,
	linux-cve-announce@...r.kernel.org
Subject: Re: CVE-2021-47326: x86/signal: Detect and prevent an alternate
 signal stack overflow

On Thu, May 23, 2024 at 01:19:17PM +0300, Nikolay Borisov wrote:
> 
> 
> On 21.05.24 г. 17:36 ч., Greg Kroah-Hartman wrote:
> > Description
> > ===========
> > 
> > In the Linux kernel, the following vulnerability has been resolved:
> > 
> > x86/signal: Detect and prevent an alternate signal stack overflow
> > 
> > The kernel pushes context on to the userspace stack to prepare for the
> > user's signal handler. When the user has supplied an alternate signal
> > stack, via sigaltstack(2), it is easy for the kernel to verify that the
> > stack size is sufficient for the current hardware context.
> > 
> > Check if writing the hardware context to the alternate stack will exceed
> > it's size. If yes, then instead of corrupting user-data and proceeding with
> > the original signal handler, an immediate SIGSEGV signal is delivered.
> > 
> > Refactor the stack pointer check code from on_sig_stack() and use the new
> > helper.
> > 
> > While the kernel allows new source code to discover and use a sufficient
> > alternate signal stack size, this check is still necessary to protect
> > binaries with insufficient alternate signal stack size from data
> > corruption.
> > 
> > The Linux kernel CVE team has assigned CVE-2021-47326 to this issue.
> 
> 
> I'd like to dispute this CVE. Basically a process can pass in a
> wrongly-sized stack which will cause its own stack to be corrupted. If
> anything this affects the process rather than the kernel.

Ah, good catch, thanks, I'll go revoke this CVE now.

Thanks for the review, much appreciated!

greg k-h