linux-kernel - include/linux/seq_file.h:247:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4

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Date:   Tue, 8 Nov 2022 07:54:41 +0800
From:   kernel test robot <lkp@...el.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: include/linux/seq_file.h:247:9: warning: 'strncpy' output may be
 truncated copying 4 bytes from a string of length 4

Hi Ilya,

FYI, the error/warning still remains.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   59f2f4b8a757412fce372f6d0767bdb55da127a8
commit: e37b3dd063a1a68e28a7cfaf77c84c472112e330 s390: enable KCSAN
date:   1 year, 3 months ago
config: s390-randconfig-r011-20221108
compiler: s390-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e37b3dd063a1a68e28a7cfaf77c84c472112e330
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout e37b3dd063a1a68e28a7cfaf77c84c472112e330
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash fs/ocfs2/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@...el.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/seq_file_net.h:5,
                    from include/net/net_namespace.h:179,
                    from include/linux/inet.h:42,
                    from fs/ocfs2/super.c:21:
   fs/ocfs2/super.c: In function 'ocfs2_show_options':
>> include/linux/seq_file.h:247:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4 [-Wstringop-truncation]
     247 |         strncpy(val_buf, value, length);                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   fs/ocfs2/super.c:1539:17: note: in expansion of macro 'seq_show_option_n'
    1539 |                 seq_show_option_n(s, "cluster_stack", osb->osb_cluster_stack,
         |                 ^~~~~~~~~~~~~~~~~


vim +/strncpy +247 include/linux/seq_file.h

a068acf2ee7769 Kees Cook 2015-09-04  233  
a068acf2ee7769 Kees Cook 2015-09-04  234  /**
a068acf2ee7769 Kees Cook 2015-09-04  235   * seq_show_option_n - display mount options with appropriate escapes
a068acf2ee7769 Kees Cook 2015-09-04  236   *		       where @value must be a specific length.
a068acf2ee7769 Kees Cook 2015-09-04  237   * @m: the seq_file handle
a068acf2ee7769 Kees Cook 2015-09-04  238   * @name: the mount option name
a068acf2ee7769 Kees Cook 2015-09-04  239   * @value: the mount option name's value, cannot be NULL
a068acf2ee7769 Kees Cook 2015-09-04  240   * @length: the length of @value to display
a068acf2ee7769 Kees Cook 2015-09-04  241   *
a068acf2ee7769 Kees Cook 2015-09-04  242   * This is a macro since this uses "length" to define the size of the
a068acf2ee7769 Kees Cook 2015-09-04  243   * stack buffer.
a068acf2ee7769 Kees Cook 2015-09-04  244   */
a068acf2ee7769 Kees Cook 2015-09-04  245  #define seq_show_option_n(m, name, value, length) {	\
a068acf2ee7769 Kees Cook 2015-09-04  246  	char val_buf[length + 1];			\
a068acf2ee7769 Kees Cook 2015-09-04 @247  	strncpy(val_buf, value, length);		\
a068acf2ee7769 Kees Cook 2015-09-04  248  	val_buf[length] = '\0';				\
a068acf2ee7769 Kees Cook 2015-09-04  249  	seq_show_option(m, name, val_buf);		\
a068acf2ee7769 Kees Cook 2015-09-04  250  }
a068acf2ee7769 Kees Cook 2015-09-04  251  

:::::: The code at line 247 was first introduced by commit
:::::: a068acf2ee77693e0bf39d6e07139ba704f461c3 fs: create and use seq_show_option for escaping

:::::: TO: Kees Cook <keescook@...omium.org>
:::::: CC: Linus Torvalds <torvalds@...ux-foundation.org>

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

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