linux-kernel - RE: [PATCH 2/3] drivers: hv: vmbus: Fix sscanf format specifier in target_cpu

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Message-ID:
 <SN6PR02MB41577DBA5D2C981ACEC4D9DED40AA@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Sun, 14 Sep 2025 04:27:19 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Alok Tiwari <alok.a.tiwari@...cle.com>, "kys@...rosoft.com"
	<kys@...rosoft.com>, "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>, "decui@...rosoft.com"
	<decui@...rosoft.com>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/3] drivers: hv: vmbus: Fix sscanf format specifier in
 target_cpu_store()

From: Alok Tiwari <alok.a.tiwari@...cle.com> Sent: Saturday, September 13, 2025 12:25 PM
> 
> The target_cpu_store() function parses the target CPU from the sysfs
> buffer using sscanf(). The format string currently uses "%uu", which
> is invalid and causes incorrect parsing.

The %uu format string definitely looks invalid, but I'm not seeing
incorrect parsing.  For example, this command works:

# echo 5 >/sys/bus/vmbus/devices/<uuid>/channels/<nn>/cpu

and the target cpu is indeed changed to "5".  A two-digit value also
works:

# echo 14 >/sys/bus/vmbus/devices/<uuid>/channels/<nn>/cpu

What are the details of the incorrect parsing that you are seeing?

Michael

> 
> Fix it by using "%u" to correctly read the value.
> 
> This only fixes the parsing format.
> 
> Signed-off-by: Alok Tiwari <alok.a.tiwari@...cle.com>
> ---
>  drivers/hv/vmbus_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 8b58306cb140..fbab9f2d7fa6 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1742,7 +1742,7 @@ static ssize_t target_cpu_store(struct vmbus_channel
> *channel,
>  	u32 target_cpu;
>  	ssize_t ret;
> 
> -	if (sscanf(buf, "%uu", &target_cpu) != 1)
> +	if (sscanf(buf, "%u", &target_cpu) != 1)
>  		return -EIO;
> 
>  	cpus_read_lock();
> --
> 2.50.1
>