linux-kernel - Re: [PATCH] therm.c: Adding an array index check before accessing an element.

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Message-ID: <5be85b32-7339-d306-897e-142332807c9b@ispras.ru>
Date: Fri, 5 Jan 2024 20:50:34 +0700
From: Alexey Khoroshilov <khoroshilov@...ras.ru>
To: Andrey Shumilin <shum.sdl@...ct.ru>, Karol Herbst <kherbst@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...hat.com>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org,
 "lvc-project@...uxtesting.org" <lvc-project@...uxtesting.org>
Subject: Re: [PATCH] therm.c: Adding an array index check before accessing an
 element.

> Subject: therm.c: Adding an array index check before accessing an element.

As

$ git log --oneline drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c
a215721fb64e drm/nouveau/bios/therm: pointers are 32-bit
46484438ab7d drm/nouveau/bios: convert to new-style nvkm_subdev
7f5f518fd70b drm/nouveau/bios: remove object accessor functions
60b29d207179 drm/nouveau/bios: switch to subdev printk macros
9ace404b1098 drm/nouveau/device: include core/device.h automatically for
subdevs/engines
d390b48027f8 drm/nouveau/bios: namespace + nvidia gpu names (no binary
change)
c39f472e9f14 drm/nouveau: remove symlinks, move core/ to nvkm/ (no code
changes)

shows, a better prefix should be
drm/nouveau/bios: or drm/nouveau/bios/therm:
and there should not be a dot at the end.

e.g.
drm/nouveau/bios: avoid invalid memory memory access in
nvbios_therm_fan_parse()

On 16.11.2023 09:30, Andrey Shumilin wrote:
> It is possible to access an element at index -1 if at the first iteration of the loop the result of switch is equal to 0x25
> 

If nvbios_rd08(bios, entry + 0) returns 0x25 before 0x24, buffer
underrun happens as far as &fan->trip[fan->nr_fan_trip - 1] points to
invalid memory.

> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Signed-off-by: Andrey Shumilin <shum.sdl@...ct.ru>
> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c b/drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c
> index 5babc5a7c7d5..78387053f214 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/bios/therm.c
> @@ -180,6 +180,8 @@ nvbios_therm_fan_parse(struct nvkm_bios *bios, struct nvbios_therm_fan *fan)
>  			cur_trip->fan_duty = duty_lut[(value & 0xf000) >> 12];
>  			break;
>  		case 0x25:
> +			if (fan->nr_fan_trip == 0)
> +				fan->nr_fan_trip++;

I would suggest to return -EINVAL if the assumption on valid nr_fan_trip
is failed.

>  			cur_trip = &fan->trip[fan->nr_fan_trip - 1];
>  			cur_trip->fan_duty = value;
>  			break;
> 

--
Alexey