maint: prohibit direct use of strncmp: prefer STREQ_LEN, STRNCMP_LIT

* cfg.mk (sc_prohibit_strncmp): New rule, mostly from libvirt.
* src/system.h (STREQ_LEN, STRPREFIX, STRNCMP_LIT): Define.
* src/df.c (get_dev, get_point): Convert.
* src/extent-scan.c (extent_need_sync): Likewise.
* src/ls.c (is_colored, decode_switches): Likewise.
(parse_ls_color, (print_color_indicator): Likewise.
* src/md5sum.c (split_3): Likewise.
* src/split.c (main, emit_ancillary_info): Likewise.
* src/tr.c (look_up_char_class): Likewise.
* src/uname.c (main): Likewise.
* src/who.c (scan_entries): Likewise.

9 files changed, 25 insertions, 18 deletions

diff --git a/src/df.c b/src/df.c
index 357dca547..14f07905d 100644
--- a/src/df.c
+++ b/src/df.c
@@ -611,9 +611,9 @@ get_dev (char const *disk, char const *mount_point,
               /* Don't print the first directory name in MOUNT_POINT if it's an
                  artifact of an automounter.  This is a bit too aggressive to be
                  the default.  */
-              if (strncmp ("/auto/", mount_point, 6) == 0)
+              if (STRNCMP_LIT (mount_point, "/auto/") == 0)
                 mount_point += 5;
-              else if (strncmp ("/tmp_mnt/", mount_point, 9) == 0)
+              else if (STRNCMP_LIT (mount_point, "/tmp_mnt/") == 0)
                 mount_point += 8;
 #endif
               cell = xstrdup (mount_point);
@@ -682,7 +682,7 @@ get_point (const char *point, const struct stat *statp)
           if (best_match_len <= len && len <= resolved_len
               && (len == 1 /* root file system */
                   || ((len == resolved_len || resolved[len] == '/')
-                      && strncmp (me->me_mountdir, resolved, len) == 0)))
+                      && STREQ_LEN (me->me_mountdir, resolved, len))))
             {
               best_match = me;
               best_match_len = len;
diff --git a/src/extent-scan.c b/src/extent-scan.c
index d84746c56..f8f8ca6dc 100644
--- a/src/extent-scan.c
+++ b/src/extent-scan.c
@@ -45,7 +45,7 @@ extent_need_sync (void)
       need_sync = 0; /* No workaround by default.  */
 
 #ifdef __linux__
-      if (uname (&name) != -1 && strncmp (name.release, "2.6.", 4) == 0)
+      if (uname (&name) != -1 && STRNCMP_LIT (name.release, "2.6.") == 0)
         {
            unsigned long val;
            if (xstrtoul (name.release + 4, NULL, 10, &val, NULL) == LONGINT_OK)
diff --git a/src/ls.c b/src/ls.c
index c09a91346..a7ea8c2cb 100644
--- a/src/ls.c
+++ b/src/ls.c
@@ -1131,8 +1131,8 @@ is_colored (enum indicator_no type)
   size_t len = color_indicator[type].len;
   char const *s = color_indicator[type].string;
   return ! (len == 0
-            || (len == 1 && strncmp (s, "0", 1) == 0)
-            || (len == 2 && strncmp (s, "00", 2) == 0));
+            || (len == 1 && STRNCMP_LIT (s, "0") == 0)
+            || (len == 2 && STRNCMP_LIT (s, "00") == 0));
 }
 
 static void
@@ -1996,7 +1996,7 @@ decode_switches (int argc, char **argv)
         if (! (style = getenv ("TIME_STYLE")))
           style = bad_cast ("locale");
 
-      while (strncmp (style, posix_prefix, sizeof posix_prefix - 1) == 0)
+      while (STREQ_LEN (style, posix_prefix, sizeof posix_prefix - 1))
         {
           if (! hard_locale (LC_TIME))
             return optind;
@@ -2388,7 +2388,7 @@ parse_ls_color (void)
     }
 
   if (color_indicator[C_LINK].len == 6
-      && !strncmp (color_indicator[C_LINK].string, "target", 6))
+      && !STRNCMP_LIT (color_indicator[C_LINK].string, "target"))
     color_symlink_as_referent = true;
 }
 
@@ -4178,7 +4178,7 @@ print_color_indicator (const struct fileinfo *f, bool symlink_target)
         }
       else if (S_ISLNK (mode))
         type = ((!linkok
-                 && (!strncmp (color_indicator[C_LINK].string, "target", 6)
+                 && (!STRNCMP_LIT (color_indicator[C_LINK].string, "target")
                      || color_indicator[C_ORPHAN].string))
                 ? C_ORPHAN : C_LINK);
       else if (S_ISFIFO (mode))
@@ -4209,8 +4209,8 @@ print_color_indicator (const struct fileinfo *f, bool symlink_target)
       for (ext = color_ext_list; ext != NULL; ext = ext->next)
         {
           if (ext->ext.len <= len
-              && strncmp (name - ext->ext.len, ext->ext.string,
-                          ext->ext.len) == 0)
+              && STREQ_LEN (name - ext->ext.len, ext->ext.string,
+                            ext->ext.len))
             break;
         }
     }
diff --git a/src/md5sum.c b/src/md5sum.c
index 697689b3b..6f6e6373d 100644
--- a/src/md5sum.c
+++ b/src/md5sum.c
@@ -262,7 +262,7 @@ split_3 (char *s, size_t s_len,
 
   /* Check for BSD-style checksum line. */
   algo_name_len = strlen (DIGEST_TYPE_STRING);
-  if (strncmp (s + i, DIGEST_TYPE_STRING, algo_name_len) == 0)
+  if (STREQ_LEN (s + i, DIGEST_TYPE_STRING, algo_name_len))
     {
       if (s[i + algo_name_len] == ' ')
         ++i;
diff --git a/src/split.c b/src/split.c
index 364576aa8..3a630a001 100644
--- a/src/split.c
+++ b/src/split.c
@@ -895,12 +895,12 @@ main (int argc, char **argv)
           /* skip any whitespace */
           while (isspace (to_uchar (*optarg)))
             optarg++;
-          if (strncmp (optarg, "r/", 2) == 0)
+          if (STRNCMP_LIT (optarg, "r/") == 0)
             {
               split_type = type_rr;
               optarg += 2;
             }
-          else if (strncmp (optarg, "l/", 2) == 0)
+          else if (STRNCMP_LIT (optarg, "l/") == 0)
             {
               split_type = type_chunk_lines;
               optarg += 2;
diff --git a/src/system.h b/src/system.h
index b86e57047..1c351bd1b 100644
--- a/src/system.h
+++ b/src/system.h
@@ -257,6 +257,13 @@ select_plural (uintmax_t n)
 }
 
 #define STREQ(a, b) (strcmp (a, b) == 0)
+#define STREQ_LEN(a, b, n) (strncmp (a, b, n) == 0)
+#define STRPREFIX(a, b) (strncmp(a, b, strlen (b)) == 0)
+
+/* Just like strncmp, but the first argument must be a literal string
+   and you don't specify the length.  */
+#define STRNCMP_LIT(s, literal) \
+  strncmp (s, "" literal "", sizeof (literal) - 1)
 
 #if !HAVE_DECL_GETLOGIN
 char *getlogin ();
@@ -607,7 +614,7 @@ emit_ancillary_info (void)
   /* Don't output this redundant message for English locales.
      Note we still output for 'C' so that it gets included in the man page.  */
   const char *lc_messages = setlocale (LC_MESSAGES, NULL);
-  if (lc_messages && strncmp (lc_messages, "en_", 3))
+  if (lc_messages && STRNCMP_LIT (lc_messages, "en_"))
     {
       /* TRANSLATORS: Replace LANG_CODE in this URL with your language code
          <http://translationproject.org/team/LANG_CODE.html> to form one of
diff --git a/src/tr.c b/src/tr.c
index 2809f8722..2a729c696 100644
--- a/src/tr.c
+++ b/src/tr.c
@@ -548,7 +548,7 @@ look_up_char_class (char const *class_str, size_t len)
   enum Char_class i;
 
   for (i = 0; i < ARRAY_CARDINALITY (char_class_name); i++)
-    if (strncmp (class_str, char_class_name[i], len) == 0
+    if (STREQ_LEN (class_str, char_class_name[i], len)
         && strlen (char_class_name[i]) == len)
       return i;
   return CC_NO_CLASS;
diff --git a/src/uname.c b/src/uname.c
index 7ed1bc85b..dd5de54e5 100644
--- a/src/uname.c
+++ b/src/uname.c
@@ -333,7 +333,7 @@ main (int argc, char **argv)
 
               /* Hack "safely" around the ppc vs. powerpc return value. */
               if (cputype == CPU_TYPE_POWERPC
-                  && strncmp (element, "ppc", 3) == 0)
+                  && STRNCMP_LIT (element, "ppc") == 0)
                 element = "powerpc";
             }
 # endif
diff --git a/src/who.c b/src/who.c
index 2a82b61bf..7449ab1b4 100644
--- a/src/who.c
+++ b/src/who.c
@@ -584,7 +584,7 @@ scan_entries (size_t n, const STRUCT_UTMP *utmp_buf)
       ttyname_b = ttyname (STDIN_FILENO);
       if (!ttyname_b)
         return;
-      if (strncmp (ttyname_b, DEV_DIR_WITH_TRAILING_SLASH, DEV_DIR_LEN) == 0)
+      if (STRNCMP_LIT (ttyname_b, DEV_DIR_WITH_TRAILING_SLASH) == 0)
         ttyname_b += DEV_DIR_LEN;	/* Discard /dev/ prefix.  */
     }