linux-kernel - Re: drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:65: warning: array subscript 'struct kvaser_cmd_ext[0]' is partly outside array bounds of 'unsigned char[32]'

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Message-ID: <20221031084119.bt73s33ps5naz4eh@pengutronix.de>
Date:   Mon, 31 Oct 2022 09:41:19 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     kernel test robot <lkp@...el.com>
Cc:     Kenneth Lee <klee33@...edu>, oe-kbuild-all@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:65:
 warning: array subscript 'struct kvaser_cmd_ext[0]' is partly outside array
 bounds of 'unsigned char[32]'

On 31.10.2022 07:35:36, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   30a0b95b1335e12efef89dd78518ed3e4a71a763
> commit: 00784da3e6b8c1f0e58d813272503d014de8f64b can: kvaser_usb: kvaser_usb_hydra: Use kzalloc for allocating only one element
> date:   8 weeks ago
> config: i386-randconfig-r021-20221031
> compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
> reproduce (this is a W=1 build):
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=00784da3e6b8c1f0e58d813272503d014de8f64b
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 00784da3e6b8c1f0e58d813272503d014de8f64b
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/byteorder/little_endian.h:5,
>                     from arch/x86/include/uapi/asm/byteorder.h:5,
>                     from include/asm-generic/bitops/le.h:6,
>                     from arch/x86/include/asm/bitops.h:416,
>                     from include/linux/bitops.h:68,
>                     from include/linux/kernel.h:22,
>                     from arch/x86/include/asm/percpu.h:27,
>                     from arch/x86/include/asm/preempt.h:6,
>                     from include/linux/preempt.h:78,
>                     from include/linux/spinlock.h:55,
>                     from include/linux/swait.h:7,
>                     from include/linux/completion.h:12,
>                     from drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:16:
>    drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c: In function 'kvaser_usb_hydra_send_simple_cmd':
> >> drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:65: warning: array subscript 'struct kvaser_cmd_ext[0]' is partly outside array bounds of 'unsigned char[32]' [-Warray-bounds]
>      489 |                 ret = le16_to_cpu(((struct kvaser_cmd_ext *)cmd)->len);
>    include/uapi/linux/byteorder/little_endian.h:37:51: note: in definition of macro '__le16_to_cpu'
>       37 | #define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
>          |                                                   ^
>    drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:489:23: note: in expansion of macro 'le16_to_cpu'
>      489 |                 ret = le16_to_cpu(((struct kvaser_cmd_ext *)cmd)->len);
>          |                       ^~~~~~~~~~~
>    drivers/net/can/usb/kvaser_usb/kvaser_usb_hydra.c:537:15: note: referencing an object of size 32 allocated by 'kzalloc'
>      537 |         cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
>          |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I think this is a false positive.

The commit you're building 00784da3e6b8 ("can: kvaser_usb:
kvaser_usb_hydra: Use kzalloc for allocating only one element") contains
3e88445a3a5a ("can: kvaser_usb: silence a GCC 12 -Warray-bounds
warning").

In the latter commit, the -Warray-bounds warning was disabled, as gcc-12
has some problem with it. However you're using gcc-11 (Debian 11.3.0-8)
11.3.0 here. Don't know the status of gcc-11 with regards to that
warning.

In the mean time in 26117d92d001 ("can: kvaser_usb: Remove
-Warray-bounds exception") that was removed, as gcc-13 should be fixed.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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