linux-kernel - include/linux/seq_file.h:262:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4

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Date:   Mon, 17 Jan 2022 04:33:03 +0800
From:   kernel test robot <lkp@...el.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>
Subject: include/linux/seq_file.h:262:9: warning: 'strncpy' output may be
 truncated copying 4 bytes from a string of length 4

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   79e06c4c4950be2abd8ca5d2428a8c915aa62c24
commit: dd03762ab608e058c8f390ad9cf667e490089796 arm64: Enable KCSAN
date:   5 weeks ago
config: arm64-buildonly-randconfig-r001-20220116 (https://download.01.org/0day-ci/archive/20220117/202201170456.6rWV7FEz-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 11.2.0
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=dd03762ab608e058c8f390ad9cf667e490089796
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout dd03762ab608e058c8f390ad9cf667e490089796
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm64 SHELL=/bin/bash drivers/char/ipmi/ drivers/pci/controller/ fs/ocfs2/

If you fix the issue, kindly add following tag as appropriate
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:181,
                    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:262:9: warning: 'strncpy' output may be truncated copying 4 bytes from a string of length 4 [-Wstringop-truncation]
     262 |         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,
         |                 ^~~~~~~~~~~~~~~~~
--
   drivers/char/ipmi/ipmi_msghandler.c: In function 'send_panic_events':
>> drivers/char/ipmi/ipmi_msghandler.c:5283:17: warning: 'strncpy' specified bound 11 equals destination size [-Wstringop-truncation]
    5283 |                 strncpy(data+5, p, 11);
         |                 ^~~~~~~~~~~~~~~~~~~~~~


vim +/strncpy +262 include/linux/seq_file.h

a068acf2ee77693 Kees Cook 2015-09-04  248  
a068acf2ee77693 Kees Cook 2015-09-04  249  /**
a068acf2ee77693 Kees Cook 2015-09-04  250   * seq_show_option_n - display mount options with appropriate escapes
a068acf2ee77693 Kees Cook 2015-09-04  251   *		       where @value must be a specific length.
a068acf2ee77693 Kees Cook 2015-09-04  252   * @m: the seq_file handle
a068acf2ee77693 Kees Cook 2015-09-04  253   * @name: the mount option name
a068acf2ee77693 Kees Cook 2015-09-04  254   * @value: the mount option name's value, cannot be NULL
a068acf2ee77693 Kees Cook 2015-09-04  255   * @length: the length of @value to display
a068acf2ee77693 Kees Cook 2015-09-04  256   *
a068acf2ee77693 Kees Cook 2015-09-04  257   * This is a macro since this uses "length" to define the size of the
a068acf2ee77693 Kees Cook 2015-09-04  258   * stack buffer.
a068acf2ee77693 Kees Cook 2015-09-04  259   */
a068acf2ee77693 Kees Cook 2015-09-04  260  #define seq_show_option_n(m, name, value, length) {	\
a068acf2ee77693 Kees Cook 2015-09-04  261  	char val_buf[length + 1];			\
a068acf2ee77693 Kees Cook 2015-09-04 @262  	strncpy(val_buf, value, length);		\
a068acf2ee77693 Kees Cook 2015-09-04  263  	val_buf[length] = '\0';				\
a068acf2ee77693 Kees Cook 2015-09-04  264  	seq_show_option(m, name, val_buf);		\
a068acf2ee77693 Kees Cook 2015-09-04  265  }
a068acf2ee77693 Kees Cook 2015-09-04  266  

:::::: The code at line 262 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, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org