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Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers

From Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Newsgroups linux.kernel
Subject Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers
Date 2017-07-14 15:00 +0200
Message-ID <u38mn-3Ag-49@gated-at.bofh.it> (permalink)
References <u37zX-3en-5@gated-at.bofh.it> <u37JE-3iP-9@gated-at.bofh.it>
Organization Intel Finland Oy

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On Fri, 2017-07-14 at 14:07 +0200, Arnd Bergmann wrote:
> gcc-7 notices that the pin_table is an array of 16-bit numbers,
> but we assume it can be printed as a two-character hexadecimal
> string:
> 
> drivers/gpio/gpiolib-acpi.c: In function
> 'acpi_gpiochip_request_interrupt':
> drivers/gpio/gpiolib-acpi.c:206:24: warning: '%02X' directive writing
> between 2 and 4 bytes into a region of size 3 [-Wformat-overflow=]
>    sprintf(ev_name, "_%c%02X",
>                         ^~~~
> drivers/gpio/gpiolib-acpi.c:206:20: note: directive argument in the
> range [0, 65535]
>    sprintf(ev_name, "_%c%02X",
>                     ^~~~~~~~~
> drivers/gpio/gpiolib-acpi.c:206:3: note: 'sprintf' output between 5
> and 7 bytes into a destination of size 5
>    sprintf(ev_name, "_%c%02X",
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>     agpio->triggering == ACPI_EDGE_SENSITIVE ? 'E' : 'L',
>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     pin);
>     ~~~~


This is obviously a false positive warning.

Here we have
int pin = u16 pin_table[0] <= 255 (implying >= 0).

I see few options how to make it more clear
1) your proposal;
2) use "%02hhX" instead;
3) use if (ret >= 0 && ret <= 255) condition.

I would choose one of the 2-3.

In case gcc will complain about 3), file a bug to gcc crazy warning.

> 
> This can't be right, so this changes it to truncate the number to
> an 8-bit pin number.
> 
> Fixes: 0d1c28a449c6 ("gpiolib-acpi: Add ACPI5 event model support to
> gpio.")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpio/gpiolib-acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpiolib-acpi.c b/drivers/gpio/gpiolib-acpi.c
> index c9b42dd12dfa..c3faea724af8 100644
> --- a/drivers/gpio/gpiolib-acpi.c
> +++ b/drivers/gpio/gpiolib-acpi.c
> @@ -205,7 +205,7 @@ static acpi_status
> acpi_gpiochip_request_interrupt(struct acpi_resource *ares,
>  		char ev_name[5];
>  		sprintf(ev_name, "_%c%02X",
>  			agpio->triggering == ACPI_EDGE_SENSITIVE ?
> 'E' : 'L',
> -			pin);
> +			(u8)pin);
>  		if (ACPI_SUCCESS(acpi_get_handle(handle, ev_name,
> &evt_handle)))
>  			handler = acpi_gpio_irq_handler;
>  	}

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy

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Thread

[PATCH 00/22] gcc-7 -Wformat-* warnings Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:10 +0200
  [PATCH 01/22] kbuild: disable -Wformat-truncation warnings by default Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:10 +0200
  [PATCH 02/22] scsi: megaraid: fix format-overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:10 +0200
  [PATCH 07/22] scsi: gdth: increase the procfs event buffer size Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin  numbers Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2017-07-14 15:00 +0200
      Re: [PATCH 18/22] gpio: acpi: fix string overflow for large pin numbers Arnd Bergmann <arnd@arndb.de> - 2017-07-14 22:00 +0200
  [PATCH 03/22] scsi: mpt3sas: fix format overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 11/22] net: thunder_bgx: avoid format string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 11/22] net: thunder_bgx: avoid format string overflow  warning Robin Murphy <robin.murphy@arm.com> - 2017-07-14 14:40 +0200
    Re: [PATCH 11/22] net: thunder_bgx: avoid format string overflow  warning David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 10/22] bnx2x: fix format overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 10/22] bnx2x: fix format overflow warning David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 21/22] fscache: fix fscache_objlist_show format processing Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning Hans Verkuil <hverkuil@xs4all.nl> - 2017-07-17 15:00 +0200
      Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-17 15:00 +0200
        Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning Hans Verkuil <hverkuil@xs4all.nl> - 2017-07-17 15:00 +0200
  [PATCH 04/22] scsi: fusion: fix string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    RE: [PATCH 04/22] scsi: fusion: fix string overflow warning David Laight <David.Laight@ACULAB.COM> - 2017-07-17 11:20 +0200
      Re: [PATCH 04/22] scsi: fusion: fix string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-17 14:10 +0200
  [PATCH 15/22] hwmon: applesmc: fix format string overflow Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 15/22] hwmon: applesmc: fix format string overflow Guenter Roeck <linux@roeck-us.net> - 2017-07-14 16:10 +0200
  [PATCH 12/22] vmxnet3: avoid format strint overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 12/22] vmxnet3: avoid format strint overflow warning David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 17/22] platform/x86: alienware-wmi: fix format string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    RE: [PATCH 17/22] platform/x86: alienware-wmi: fix format string  overflow warning <Mario.Limonciello@dell.com> - 2017-07-14 20:40 +0200
    Re: [PATCH 17/22] platform/x86: alienware-wmi: fix format string  overflow warning Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-14 21:20 +0200
      Re: [PATCH 17/22] platform/x86: alienware-wmi: fix format string  overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 21:40 +0200
        Re: [PATCH 17/22] platform/x86: alienware-wmi: fix format string  overflow warning Andy Shevchenko <andy.shevchenko@gmail.com> - 2017-07-14 21:50 +0200
  [PATCH 05/22] scsi: gdth: avoid buffer overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 09/22] net: niu: fix format string overflow warning: Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 09/22] net: niu: fix format string overflow warning: David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 08/22] isdn: divert: fix sprintf buffer overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 08/22] isdn: divert: fix sprintf buffer overflow warning David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 16/22] x86: intel-mid: fix a format string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 06/22] scsi: fnic: fix format string overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
  [PATCH 22/22] IB/mlx4: fix sprintf format warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 22/22] IB/mlx4: fix sprintf format warning Leon Romanovsky <leon@kernel.org> - 2017-07-14 15:50 +0200
  [PATCH 20/22] sound: pci: avoid string overflow warnings Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 20/22] sound: pci: avoid string overflow warnings Takashi Iwai <tiwai@suse.de> - 2017-07-14 14:30 +0200
  [PATCH 13/22] liquidio: fix possible eeprom format string overflow Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200
    Re: [PATCH 13/22] liquidio: fix possible eeprom format string  overflow David Miller <davem@davemloft.net> - 2017-07-14 18:10 +0200
  [PATCH 19/22] block: DAC960: shut up format-overflow warning Arnd Bergmann <arnd@arndb.de> - 2017-07-14 14:20 +0200

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