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

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Date: Tue, 16 Jan 2024 19:36:41 +0000
From: Chris Down <chris@...isdown.name>
To: Petr Mladek <pmladek@...e.com>
Cc: "James E . J . Bottomley" <jejb@...ux.ibm.com>,
	"Martin K . Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	oe-kbuild-all@...ts.linux.dev, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] scsi: core: Safe warning about bad dev info string

Petr Mladek writes:
>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.

Acked-by: Chris Down <chris@...isdown.name>

While I agree with the other thread that in reality this is ok, it's worth 
reducing the addition to LKP noise for now and worrying about that later.

Thanks!

>
>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,
>-- 
>2.43.0
>