include/linux/seq_file.h:263:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4

[kernel test robot <lkp@intel.com>]

Hi Rohan,

FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   0b5547c51827e053cc754db47d3ec3e6c2c451d2
commit: 95567f46b4d20c047750a5e3029461afcdc67697 powerpc/{32,book3e}: kcsan: Extend KCSAN Support
date:   7 weeks ago
config: powerpc-randconfig-r015-20230725 (https://download.01.org/0day-ci/archive/20230725/202307251906.lXcLGKvG-lkp@intel.com/config)
compiler: powerpc-linux-gcc (GCC) 12.3.0
reproduce: (https://download.01.org/0day-ci/archive/20230725/202307251906.lXcLGKvG-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202307251906.lXcLGKvG-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/seq_file_net.h:5,
                    from include/net/net_namespace.h:193,
                    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:263:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4 [-Wstringop-truncation]
     263 |         strncpy(val_buf, value, length);                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   fs/ocfs2/super.c:1518:17: note: in expansion of macro 'seq_show_option_n'
    1518 |                 seq_show_option_n(s, "cluster_stack", osb->osb_cluster_stack,
         |                 ^~~~~~~~~~~~~~~~~


vim +/strncpy +263 include/linux/seq_file.h

a068acf2ee7769 Kees Cook 2015-09-04  249  
a068acf2ee7769 Kees Cook 2015-09-04  250  /**
a068acf2ee7769 Kees Cook 2015-09-04  251   * seq_show_option_n - display mount options with appropriate escapes
a068acf2ee7769 Kees Cook 2015-09-04  252   *		       where @value must be a specific length.
a068acf2ee7769 Kees Cook 2015-09-04  253   * @m: the seq_file handle
a068acf2ee7769 Kees Cook 2015-09-04  254   * @name: the mount option name
a068acf2ee7769 Kees Cook 2015-09-04  255   * @value: the mount option name's value, cannot be NULL
a068acf2ee7769 Kees Cook 2015-09-04  256   * @length: the length of @value to display
a068acf2ee7769 Kees Cook 2015-09-04  257   *
a068acf2ee7769 Kees Cook 2015-09-04  258   * This is a macro since this uses "length" to define the size of the
a068acf2ee7769 Kees Cook 2015-09-04  259   * stack buffer.
a068acf2ee7769 Kees Cook 2015-09-04  260   */
a068acf2ee7769 Kees Cook 2015-09-04  261  #define seq_show_option_n(m, name, value, length) {	\
a068acf2ee7769 Kees Cook 2015-09-04  262  	char val_buf[length + 1];			\
a068acf2ee7769 Kees Cook 2015-09-04 @263  	strncpy(val_buf, value, length);		\
a068acf2ee7769 Kees Cook 2015-09-04  264  	val_buf[length] = '\0';				\
a068acf2ee7769 Kees Cook 2015-09-04  265  	seq_show_option(m, name, val_buf);		\
a068acf2ee7769 Kees Cook 2015-09-04  266  }
a068acf2ee7769 Kees Cook 2015-09-04  267  

:::::: The code at line 263 was first introduced by commit
:::::: a068acf2ee77693e0bf39d6e07139ba704f461c3 fs: create and use seq_show_option for escaping

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

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