linux-kernel - Re: net/8021q/vlan.c:241:46: warning: '%.4i' directive output may be truncated writing between 4 and 5 bytes into a region of size between 0 and 15

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Message-ID: <3008ca8d-e599-437b-8f1e-0dbe86202f38@redhat.com>
Date: Mon, 10 Feb 2025 09:24:58 -0500
From: Waiman Long <llong@...hat.com>
To: kernel test robot <lkp@...el.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
 "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: net/8021q/vlan.c:241:46: warning: '%.4i' directive output may be
 truncated writing between 4 and 5 bytes into a region of size between 0 and
 15

On 2/9/25 11:44 PM, kernel test robot wrote:
> Hi Waiman,
>
> FYI, the error/warning still remains.
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   a64dcfb451e254085a7daee5fe51bf22959d52d3
> commit: 925da92ba5cb0c82d07cdd5049a07e40f54e9c44 rcu: Avoid unneeded function call in rcu_read_unlock()
> date:   3 years, 5 months ago
> config: sparc-randconfig-r122-20240116 (https://download.01.org/0day-ci/archive/20250210/202502101253.TDZbCYh6-lkp@intel.com/config)
> compiler: sparc-linux-gcc (GCC) 12.4.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250210/202502101253.TDZbCYh6-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202502101253.TDZbCYh6-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>     net/8021q/vlan.c: In function 'vlan_ioctl_handler':
>     net/8021q/vlan.c:253:46: warning: '%i' directive output may be truncated writing between 1 and 5 bytes into a region of size between 0 and 15 [-Wformat-truncation=]
>       253 |                 snprintf(name, IFNAMSIZ, "%s.%i", real_dev->name, vlan_id);
>           |                                              ^~
>     In function 'register_vlan_device',
>         inlined from 'vlan_ioctl_handler' at net/8021q/vlan.c:628:9:
>     net/8021q/vlan.c:253:42: note: directive argument in the range [0, 65535]
>       253 |                 snprintf(name, IFNAMSIZ, "%s.%i", real_dev->name, vlan_id);
>           |                                          ^~~~~~~
>     net/8021q/vlan.c:253:17: note: 'snprintf' output between 3 and 22 bytes into a destination of size 16
>       253 |                 snprintf(name, IFNAMSIZ, "%s.%i", real_dev->name, vlan_id);
>           |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     net/8021q/vlan.c: In function 'vlan_ioctl_handler':
>>> net/8021q/vlan.c:241:46: warning: '%.4i' directive output may be truncated writing between 4 and 5 bytes into a region of size between 0 and 15 [-Wformat-truncation=]
>       241 |                 snprintf(name, IFNAMSIZ, "%s.%.4i", real_dev->name, vlan_id);
>           |                                              ^~~~
>     In function 'register_vlan_device',
>         inlined from 'vlan_ioctl_handler' at net/8021q/vlan.c:628:9:
>     net/8021q/vlan.c:241:42: note: directive argument in the range [0, 65535]
>       241 |                 snprintf(name, IFNAMSIZ, "%s.%.4i", real_dev->name, vlan_id);
>           |                                          ^~~~~~~~~
>     net/8021q/vlan.c:241:17: note: 'snprintf' output between 6 and 22 bytes into a destination of size 16
>       241 |                 snprintf(name, IFNAMSIZ, "%s.%.4i", real_dev->name, vlan_id);
>           |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
> vim +241 net/8021q/vlan.c

Why me? I have never touched net/8021q/vlan.c and I don't believe commit 
925da92ba5cb ("rcu: Avoid unneeded function call in rcu_read_unlock()") 
has anything to do with the snprintf format warnings.

Regards,
Longman