win32: allow for trailing separator in PATH

In recent versions of Windows the PATH environment variable has
a trailing semicolon.  This is insignificant to Windows because
it's ignored.  busybox-w32 conforms to the POSIX interpretation
of PATH which treats an empty path element as denoting the current
directory.  As result, on these versions of Windows executables
may by default be run from the current directory, contrary to
usual Unix practice.

Attempt to detect and remove the trailing semicolon on applet
start up.  If the user insists, they can add a trailing semicolon
to the shell variable PATH and it will be respected in the
conventional manner.

Adds 88-112 bytes.

(GitHub issue #422)

include/mingw.h

@@ -638,3 +638,4 @@ char *get_user_name(void);
 char *quote_arg(const char *arg);
 char *find_first_executable(const char *name);
 char *xappendword(const char *str, const char *word);
+int windows_env(void);

libbb/appletlib.c

@@ -1410,6 +1410,18 @@ int main(int argc UNUSED_PARAM, char **argv)
 		if (s)
 			*s = '\0';
 	}
+
+	if (windows_env()) {
+		/* remove single trailing separator from PATH */
+		for (char **envp = environ; envp && *envp; envp++) {
+			if (is_prefixed_with_case(*envp, "PATH=")) {
+				char *end = last_char_is(*envp, ';');
+				if (end && end[-1] != ';')
+					*end = '\0';
+				break;
+			}
+		}
+	}
 # endif
 	applet_name = bb_basename(applet_name);
 

shell/ash.c

@@ -15885,30 +15885,6 @@ static void setvar_if_unset(const char *key, const char *value)
 }
 #endif
 
-#if ENABLE_PLATFORM_MINGW32
-/*
- * Detect if the environment contains certain mixed-case names:
- *
- *   Path          is present in a standard Windows environment
- *   ComSpec       is present in WINE
- *   ProgramData   is present in Cygwin/MSYS2
- */
-static int mixed_case_special_name(const char *envp)
-{
-	const char *names = "PATH=\0""COMSPEC=\0""PROGRAMDATA=\0";
-	const char *n;
-
-	for (n = names; *n; ) {
-		if (is_prefixed_with_case(envp, n) && !is_prefixed_with(envp, n)) {
-			return TRUE;
-		}
-		while (*n++)
-			;
-	}
-	return FALSE;
-}
-#endif
-
 /* Don't inline: conserve stack of caller from having our locals too */
 static NOINLINE void
 init(void)
@@ -15941,26 +15917,20 @@ init(void)
 		 * We may end up having both Path and PATH. Then Path will be chosen
 		 * because it appears first.
 		 */
-		for (envp = environ; envp && *envp; envp++) {
-			if (mixed_case_special_name(*envp)) {
-				/* mintty sets HOME:  unset it */
-				const char *tty = getenv("TERM_PROGRAM");
-				if (tty && strcmp(tty, "mintty") == 0) {
-					unsetenv("HOME");
-				}
-				break;
-			}
-		}
-
-		if (envp && *envp) {
+		if (windows_env()) {
 			/*
-			 * If we get here it's because the environment contains a path
-			 * variable called something other than PATH.  This suggests we
+			 * If we get here it's because the environment suggests we
 			 * haven't been invoked from an earlier instance of BusyBox.
 			 */
 			char *start, *end;
 			struct passwd *pw;
 
+			/* mintty sets HOME:  unset it */
+			const char *tty = getenv("TERM_PROGRAM");
+			if (tty && strcmp(tty, "mintty") == 0) {
+				unsetenv("HOME");
+			}
+
 			import = VIMPORT;
 			for (envp = environ; envp && *envp; envp++) {
 				if (!(end=strchr(*envp, '=')))

win32/mingw.c

@@ -2464,3 +2464,29 @@ char *xappendword(const char *str, const char *word)
 	free((void *)str);
 	return newstr;
 }
+
+/*
+ * Detect if the environment contains certain mixed-case names:
+ *
+ *   Path          is present in a standard Windows environment
+ *   ComSpec       is present in WINE
+ *   ProgramData   is present in Cygwin/MSYS2
+ */
+int
+windows_env(void)
+{
+	const char *names = "PATH=\0""COMSPEC=\0""PROGRAMDATA=\0";
+	const char *n;
+
+	for (char **envp = environ; envp && *envp; envp++) {
+		for (n = names; *n; ) {
+			if (is_prefixed_with_case(*envp, n) &&
+						!is_prefixed_with(*envp, n)) {
+				return TRUE;
+			}
+			while (*n++)
+				;
+		}
+	}
+	return FALSE;
+}