linux-kernel - Re: [PATCH] scsi: core: Safe warning about bad dev info string

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Date: Thu, 11 Jan 2024 09:55:54 -0800
From: Bart Van Assche <bvanassche@....org>
To: Petr Mladek <pmladek@...e.com>,
 "James E . J . Bottomley" <jejb@...ux.ibm.com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
 Chris Down <chris@...isdown.name>, oe-kbuild-all@...ts.linux.dev,
 kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] scsi: core: Safe warning about bad dev info string

On 1/11/24 08:24, Petr Mladek wrote:
> Both "model" and "strflags" are passed to "%s" even when one or both
> are NULL.
> 
> It is safe because vsprintf() would detect the NULL pointer and print
> "(null)". But it is a kernel-specific feature and compiler warns
> about it:
> 
> <warning>
>     In file included from include/linux/kernel.h:19,
>                      from arch/x86/include/asm/percpu.h:27,
>                      from arch/x86/include/asm/current.h:6,
>                      from include/linux/sched.h:12,
>                      from include/linux/blkdev.h:5,
>                      from drivers/scsi/scsi_devinfo.c:3:
>     drivers/scsi/scsi_devinfo.c: In function 'scsi_dev_info_list_add_str':
>>> include/linux/printk.h:434:44: warning: '%s' directive argument is null [-Wformat-overflow=]
>       434 | #define printk(fmt, ...) printk_index_wrap(_printk, fmt, ##__VA_ARGS__)
>           |                                            ^
>     include/linux/printk.h:430:3: note: in definition of macro 'printk_index_wrap'
>       430 |   _p_func(_fmt, ##__VA_ARGS__);    \
>           |   ^~~~~~~
>     drivers/scsi/scsi_devinfo.c:551:4: note: in expansion of macro 'printk'
>       551 |    printk(KERN_ERR "%s: bad dev info string '%s' '%s'"
>           |    ^~~~~~
>     drivers/scsi/scsi_devinfo.c:552:14: note: format string is defined here
>       552 |           " '%s'\n", __func__, vendor, model,
>           |              ^~
> </warning>
> 
> Do not rely on the kernel specific behavior and print the message a safe way.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202401112002.AOjwMNM0-lkp@intel.com/
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
> Note: The patch is only compile tested.
> 
>   drivers/scsi/scsi_devinfo.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
> index 3fcaf10a9dfe..ba7237e83863 100644
> --- a/drivers/scsi/scsi_devinfo.c
> +++ b/drivers/scsi/scsi_devinfo.c
> @@ -551,9 +551,9 @@ static int scsi_dev_info_list_add_str(char *dev_list)
>   		if (model)
>   			strflags = strsep(&next, next_check);
>   		if (!model || !strflags) {
> -			printk(KERN_ERR "%s: bad dev info string '%s' '%s'"
> -			       " '%s'\n", __func__, vendor, model,
> -			       strflags);
> +			pr_err("%s: bad dev info string '%s' '%s' '%s'\n",
> +			       __func__, vendor, model ? model : "",
> +			       strflags ? strflags : "");
>   			res = -EINVAL;
>   		} else
>   			res = scsi_dev_info_list_add(0 /* compatible */, vendor,

Expressions like "model ? model : """ can be shortened into "model ? : """.

Anyway:

Reviewed-by: Bart Van Assche <bvanassche@....org>