linux-kernel - [PATCH v1 1/1] seq_file: Replace strncpy()+nul by strscpy()

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Date:   Mon, 17 Jul 2023 12:33:32 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>
Subject: [PATCH v1 1/1] seq_file: Replace strncpy()+nul by strscpy()

Privided seq_show_option_n() macro breaks build with -Werror
and W=1, e.g.:

In function ‘strncpy’,
    inlined from ‘ocfs2_show_options’ at fs/ocfs2/super.c:1520:3:
include/linux/fortify-string.h:68:33: error: ‘__builtin_strncpy’ output may be truncated copying 4 bytes from a string of length 4 [-Werror=stringop-truncation]
   68 | #define __underlying_strncpy    __builtin_strncpy
      |                                 ^
include/linux/fortify-string.h:151:16: note: in expansion of macro ‘__underlying_strncpy’
  151 |         return __underlying_strncpy(p, q, size);
      |                ^~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

While -Werror wasn't enabled by default at the time of the original code
landed into mainline, strscpy() was already there and preferred over strncpy().
Due to above mentioned issues, use the latter in seq_show_option_n().

Fixes: a068acf2ee77 ("fs: create and use seq_show_option for escaping")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 include/linux/seq_file.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index bd023dd38ae6..e87d635ca24f 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -260,8 +260,7 @@ static inline void seq_show_option(struct seq_file *m, const char *name,
  */
 #define seq_show_option_n(m, name, value, length) {	\
 	char val_buf[length + 1];			\
-	strncpy(val_buf, value, length);		\
-	val_buf[length] = '\0';				\
+	strscpy(val_buf, value, sizeof(val_buf));	\
 	seq_show_option(m, name, val_buf);		\
 }
 
-- 
2.40.0.1.gaa8946217a0b