Re: [PATCH] thermal: core: Move initial num_trips assignment before memcpy()

[Lukasz Luba <lukasz.luba@arm.com>]

Hi Nathan,

On 2/27/24 00:54, 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
>    [    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().

I don't know this tool (yet), but this description doesn't help to
understand it better.

In the memcpy() the 'num_trips' is used not 'tz->num_trips' and
'num_trips' is set in the function argument.

> 
> Move the num_trips assignment before the memcpy() to resolve the panic
> and ensure that the fortify checks work properly.

I don't see how this change can impact the code not this tool.

> 
> Fixes: 9b0a62758665 ("thermal: core: Store zone trips table in struct thermal_zone_device")
> Signed-off-by: Nathan Chancellor <nathan@kernel.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));
>   
>   	thermal_set_delay_jiffies(&tz->passive_delay_jiffies, passive_delay);
>   	thermal_set_delay_jiffies(&tz->polling_delay_jiffies, polling_delay);
> 
> ---
> base-commit: a85739c8c6894c3b9ff860e79e91db44cb59bd63
> change-id: 20240226-thermal-fix-fortify-panic-num_trips-5f94094fb963
> 
> Best regards,

Maybe it reports different issue. There is some corner case when the
num_trips is 0. It's called from
thermal_tripless_zone_device_register().
Does your code is triggered from that function?
(you've cut the call stack so I cannot see this there)

Regards,
Lukasz