linux-hardening - Re: [PATCH] thermal: core: Move initial num

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Date: Tue, 27 Feb 2024 12:07:43 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Kees Cook <keescook@...omium.org>, Nathan Chancellor <nathan@...nel.org>
Cc: daniel.lezcano@...aro.org, rui.zhang@...el.com, lukasz.luba@....com, 
	gustavoars@...nel.org, morbo@...gle.com, justinstitt@...gle.com, 
	stanislaw.gruszka@...ux.intel.com, linux-pm@...r.kernel.org, 
	linux-hardening@...r.kernel.org, llvm@...ts.linux.dev, 
	patches@...ts.linux.dev
Subject: Re: [PATCH] thermal: core: Move initial num_trips assignment before memcpy()

On Tue, Feb 27, 2024 at 3:08 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Feb 26, 2024 at 05:54:58PM -0700, Nathan Chancellor wrote:
> > When booting a CONFIG_FORTIFY_SOURCE=y kernel compiled with a toolchain
> > that supports __counted_by() (such as clang-18 and newer), there is a
> > panic on boot:
> >
> >   [    2.913770] memcpy: detected buffer overflow: 72 byte write of buffer size 0
>
> Yay, the "better details" output is working. :)
>
> >   [    2.920834] WARNING: CPU: 2 PID: 1 at lib/string_helpers.c:1027 __fortify_report+0x5c/0x74
> >   ...
> >   [    3.039208] Call trace:
> >   [    3.041643]  __fortify_report+0x5c/0x74
> >   [    3.045469]  __fortify_panic+0x18/0x20
> >   [    3.049209]  thermal_zone_device_register_with_trips+0x4c8/0x4f8
> >
> > This panic occurs because trips is counted by num_trips but num_trips is
> > assigned after the call to memcpy(), so the fortify checks think the
> > buffer size is zero because tz was allocated with kzalloc().
> >
> > Move the num_trips assignment before the memcpy() to resolve the panic
> > and ensure that the fortify checks work properly.
> >
> > Fixes: 9b0a62758665 ("thermal: core: Store zone trips table in struct thermal_zone_device")
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> >  drivers/thermal/thermal_core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > index bb21f78b4bfa..1eabc8ebe27d 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -1354,8 +1354,8 @@ thermal_zone_device_register_with_trips(const char *type,
> >
> >       tz->device.class = thermal_class;
> >       tz->devdata = devdata;
> > -     memcpy(tz->trips, trips, num_trips * sizeof(*trips));
> >       tz->num_trips = num_trips;
> > +     memcpy(tz->trips, trips, num_trips * sizeof(*trips));
>
> Looks good to me; thanks for catching this!
>
> Reviewed-by: Kees Cook <keescook@...omium.org>

Applied, thanks!