[ammarfaizi2-block:rostedt/linux-trace/ftrace/core 33/41] include/linux/fortify-string.h:47:30: warning: '__builtin_strncat' output truncated before terminating nul copying as many bytes from a string as its length

[ammarfaizi2-block:rostedt/linux-trace/ftrace/core 33/41] include/linux/fortify-string.h:47:30: warning: '__builtin_strncat' output truncated before terminating nul copying as many bytes from a string as its length

[kernel test robot]

tree:   https://github.com/ammarfaizi2/linux-block rostedt/linux-trace/ftrace/core
head:   7ab34c09507b05b91207c596490e3b6c935b7b97
commit: 9f8e5aee93ed2482638d577a56806b455084b595 [33/41] tracing: Fix allocation of last_cmd in last_cmd_set()
config: x86_64-rhel-8.3 (https://download.01.org/0day-ci/archive/20220308/202203082112.Iu7tvFl4-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/ammarfaizi2/linux-block/commit/9f8e5aee93ed2482638d577a56806b455084b595
        git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
        git fetch --no-tags ammarfaizi2-block rostedt/linux-trace/ftrace/core
        git checkout 9f8e5aee93ed2482638d577a56806b455084b595
        # save the config file to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/trace/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/string.h:253,
                    from include/linux/bitmap.h:11,
                    from include/linux/cpumask.h:12,
                    from arch/x86/include/asm/cpumask.h:5,
                    from arch/x86/include/asm/msr.h:11,
                    from arch/x86/include/asm/processor.h:22,
                    from arch/x86/include/asm/timex.h:5,
                    from include/linux/timex.h:65,
                    from include/linux/time32.h:13,
                    from include/linux/time.h:60,
                    from include/linux/stat.h:19,
                    from include/linux/module.h:13,
                    from kernel/trace/trace_events_hist.c:8:
   In function 'strncat',
       inlined from 'last_cmd_set' at kernel/trace/trace_events_hist.c:760:2,
       inlined from 'event_hist_trigger_parse' at kernel/trace/trace_events_hist.c:6191:3:
>> include/linux/fortify-string.h:47:30: warning: '__builtin_strncat' output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]
      47 | #define __underlying_strncat __builtin_strncat
         |                              ^
   include/linux/fortify-string.h:191:10: note: in expansion of macro '__underlying_strncat'
     191 |   return __underlying_strncat(p, q, count);
         |          ^~~~~~~~~~~~~~~~~~~~
   kernel/trace/trace_events_hist.c: In function 'event_hist_trigger_parse':
   include/linux/fortify-string.h:46:29: note: length computed here
      46 | #define __underlying_strlen __builtin_strlen
         |                             ^
   include/linux/fortify-string.h:102:10: note: in expansion of macro '__underlying_strlen'
     102 |   return __underlying_strlen(p);
         |          ^~~~~~~~~~~~~~~~~~~


vim +/__builtin_strncat +47 include/linux/fortify-string.h

3009f891bb9f32 Kees Cook      2021-08-02  26  
a28a6e860c6cf2 Francis Laniel 2021-02-25  27  #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
a28a6e860c6cf2 Francis Laniel 2021-02-25  28  extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
a28a6e860c6cf2 Francis Laniel 2021-02-25  29  extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
a28a6e860c6cf2 Francis Laniel 2021-02-25  30  extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
a28a6e860c6cf2 Francis Laniel 2021-02-25  31  extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
a28a6e860c6cf2 Francis Laniel 2021-02-25  32  extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
a28a6e860c6cf2 Francis Laniel 2021-02-25  33  extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
a28a6e860c6cf2 Francis Laniel 2021-02-25  34  extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
a28a6e860c6cf2 Francis Laniel 2021-02-25  35  extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
a28a6e860c6cf2 Francis Laniel 2021-02-25  36  extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
a28a6e860c6cf2 Francis Laniel 2021-02-25  37  extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
a28a6e860c6cf2 Francis Laniel 2021-02-25  38  #else
a28a6e860c6cf2 Francis Laniel 2021-02-25  39  #define __underlying_memchr	__builtin_memchr
a28a6e860c6cf2 Francis Laniel 2021-02-25  40  #define __underlying_memcmp	__builtin_memcmp
a28a6e860c6cf2 Francis Laniel 2021-02-25  41  #define __underlying_memcpy	__builtin_memcpy
a28a6e860c6cf2 Francis Laniel 2021-02-25  42  #define __underlying_memmove	__builtin_memmove
a28a6e860c6cf2 Francis Laniel 2021-02-25  43  #define __underlying_memset	__builtin_memset
a28a6e860c6cf2 Francis Laniel 2021-02-25  44  #define __underlying_strcat	__builtin_strcat
a28a6e860c6cf2 Francis Laniel 2021-02-25  45  #define __underlying_strcpy	__builtin_strcpy
a28a6e860c6cf2 Francis Laniel 2021-02-25  46  #define __underlying_strlen	__builtin_strlen
a28a6e860c6cf2 Francis Laniel 2021-02-25 @47  #define __underlying_strncat	__builtin_strncat
a28a6e860c6cf2 Francis Laniel 2021-02-25  48  #define __underlying_strncpy	__builtin_strncpy
a28a6e860c6cf2 Francis Laniel 2021-02-25  49  #endif
a28a6e860c6cf2 Francis Laniel 2021-02-25  50  

:::::: The code at line 47 was first introduced by commit
:::::: a28a6e860c6cf231cf3c5171c75c342adcd00406 string.h: move fortified functions definitions in a dedicated header.

:::::: TO: Francis Laniel <laniel_francis@privacyrequired.com>
:::::: CC: Linus Torvalds <torvalds@linux-foundation.org>

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [ammarfaizi2-block:rostedt/linux-trace/ftrace/core 33/41] include/linux/fortify-string.h:47:30: warning: '__builtin_strncat' output truncated before terminating nul copying as many bytes from a string as its length

[Steven Rostedt]

On Tue, 8 Mar 2022 21:15:29 +0800
kernel test robot <lkp@intel.com> wrote:

> All warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/string.h:253,
>                     from include/linux/bitmap.h:11,
>                     from include/linux/cpumask.h:12,
>                     from arch/x86/include/asm/cpumask.h:5,
>                     from arch/x86/include/asm/msr.h:11,
>                     from arch/x86/include/asm/processor.h:22,
>                     from arch/x86/include/asm/timex.h:5,
>                     from include/linux/timex.h:65,
>                     from include/linux/time32.h:13,
>                     from include/linux/time.h:60,
>                     from include/linux/stat.h:19,
>                     from include/linux/module.h:13,
>                     from kernel/trace/trace_events_hist.c:8:
>    In function 'strncat',
>        inlined from 'last_cmd_set' at kernel/trace/trace_events_hist.c:760:2,
>        inlined from 'event_hist_trigger_parse' at kernel/trace/trace_events_hist.c:6191:3:
> >> include/linux/fortify-string.h:47:30: warning: '__builtin_strncat' output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]  
>       47 | #define __underlying_strncat __builtin_strncat
>          |                              ^
>    include/linux/fortify-string.h:191:10: note: in expansion of macro '__underlying_strncat'
>      191 |   return __underlying_strncat(p, q, count);
>          |          ^~~~~~~~~~~~~~~~~~~~
>    kernel/trace/trace_events_hist.c: In function 'event_hist_trigger_parse':
>    include/linux/fortify-string.h:46:29: note: length computed here
>       46 | #define __underlying_strlen __builtin_strlen
>          |                             ^
>    include/linux/fortify-string.h:102:10: note: in expansion of macro '__underlying_strlen'
>      102 |   return __underlying_strlen(p);
>          |          ^~~~~~~~~~~~~~~~~~~

I see my mistake. The code it's talking about is this:

	len = sizeof(HIST_PREFIX) + strlen(str) + 1;
	kfree(last_cmd);
	last_cmd = kzalloc(len, GFP_KERNEL);
	if (!last_cmd)
		return;

	strcpy(last_cmd, HIST_PREFIX);
	len -= sizeof(HIST_PREFIX) + 1;
	strncat(last_cmd, str, len);


Where according to the man page of strncat:

     If src contains n or more bytes, strncat() writes n+1 bytes to dest (n
     from src plus the terminating null byte).  Therefore, the size of dest
     must be at least strlen(dest)+n+1.

The above did: len -= sizeof(HIST_PREFIX) + 1; when it meant to do:

  len -= strlen(HIST_PREFX) + 1

Or it could just do:

  len -= sizeof(HIST_PREFIX)

as sizeof(HIST_PREFIX) contains the nul byte.

Heck, the allocation could be:

	len = sizeof(HIST_PREFIX) + strlen(str);

As the sizeof already contains the nul byte.

Will fix.

Thanks,

-- Steve