Cygwin: mount: differ allowed server name chars from allowed share name chars

The list of invalid chars for server names differs from the
list of invalid chars for share names.  Apart from that,
we don't allow control chars in both kinds of names.

Fixes: 6338d2f24a ("Cygwin: mount: allow any valid character in UNC paths")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/mount.cc

@@ -51,10 +51,23 @@ int NO_COPY mount_info::root_idx = -1;
    This function is only used to test for valid input strings.
    The later normalization drops the native prefixes. */
 
+/* list of invalid chars in server names.  Note that underscore is ok,
+   but it cripples interoperability. */
+const char _invalid_server_char[] = ",~:!@#$%^&'.(){} ";
+#define valid_server_char(_c)	({				\
+		const char __c = (_c);				\
+		!iscntrl(__c)					\
+		&& strchr (_invalid_server_char, (_c)) == NULL;	\
+	})
+
 /* list of invalid chars in UNC filenames.  These are a few more than
    for "normal" filenames. */
-const char _invalid_char[] = "\"/\\[]:|<>+=;,?*";
-#define valid_share_char(_c)	(strchr (_invalid_char, (_c)) == NULL)
+const char _invalid_share_char[] = "\"/\\[]:|<>+=;,?*";
+#define valid_share_char(_c)	({				\
+		const char __c = (_c);				\
+		!iscntrl(__c)					\
+		&& strchr (_invalid_share_char, __c) == NULL;	\
+	})
 
 static inline bool
 is_native_path (const char *path)
@@ -72,7 +85,7 @@ is_unc_share (const char *path)
   const char *p;
   return (isdirsep (path[0])
 	 && isdirsep (path[1])
-	 && valid_share_char (path[2])
+	 && valid_server_char (path[2])
 	 && ((p = strpbrk (path + 3, "\\/")) != NULL)
 	 && valid_share_char (p[1]));
 }