linux-kernel - Re: [PATCH] kobject_uevent: Fix OOB access within zap_modalias

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Date: Fri, 24 May 2024 08:56:50 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: quic_zijuhu <quic_zijuhu@...cinc.com>
Cc: rafael@...nel.org, akpm@...ux-foundation.org, dmitry.torokhov@...il.com,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] kobject_uevent: Fix OOB access within zap_modalias_env()

On Fri, May 24, 2024 at 01:34:49PM +0800, quic_zijuhu wrote:
> On 5/24/2024 1:21 PM, Greg KH wrote:
> > On Fri, May 24, 2024 at 01:15:01PM +0800, quic_zijuhu wrote:
> >> On 5/24/2024 12:33 PM, Greg KH wrote:
> >>> On Fri, May 24, 2024 at 12:20:03PM +0800, Zijun Hu wrote:
> >>>> zap_modalias_env() wrongly calculates size of memory block
> >>>> to move, so maybe cause OOB memory access issue, fixed by
> >>>> correcting size to memmove.
> >>>
> >>> "maybe" or "does"?  That's a big difference :)
> >>>
> >> i found this issue by reading code instead of really meeting this issue.
> >> this issue should be prone to happen if there are more than 1 other
> >> environment vars.
> > 
> > But does it?  Given that we have loads of memory checkers, and I haven't
> > ever seen any report of any overrun, it would be nice to be sure.
> > 
> yes. if @env includes env vairable MODALIAS and  more than one other env
> vairables. then (env->buflen - len) must be greater that actual size of
> "target block" shown previously, so the OOB issue must happen.

Then why are none of the tools that we have for catching out-of-bound
issues triggered here?  Are the tools broken or is this really just not
ever happening?  It would be good to figure that out...

thanks,

greg k-h