Sanitise bad characters in log file names.

On Windows, colons are illegal in filenames, because they're part of
the path syntax. But colons can appear in automatically constructed
log file names, if an IPv6 address is expanded from the &H placeholder.

Now we coerce any such illegal characters to '.', which is a bit of a
bodge but should at least cause a log file to be generated.

(cherry picked from commit 64ec5e03d5)

logging.c

@@ -446,6 +446,7 @@ static Filename *xlatlognam(Filename *src, char *hostname, int port,
     s = filename_to_str(src);
 
     while (*s) {
+        int sanitise = FALSE;
 	/* Let (bufp, len) be the string to append. */
 	bufp = buf;		       /* don't usually override this */
 	if (*s == '&') {
@@ -478,6 +479,12 @@ static Filename *xlatlognam(Filename *src, char *hostname, int port,
 		if (c != '&')
 		    buf[size++] = c;
 	    }
+            /* Never allow path separators - or any other illegal
+             * filename character - to come out of any of these
+             * auto-format directives. E.g. 'hostname' can contain
+             * colons, if it's an IPv6 address, and colons aren't
+             * legal in filenames on Windows. */
+            sanitise = TRUE;
 	} else {
 	    buf[0] = *s++;
 	    size = 1;
@@ -486,8 +493,12 @@ static Filename *xlatlognam(Filename *src, char *hostname, int port,
             bufsize = (buflen + size) * 5 / 4 + 512;
             buffer = sresize(buffer, bufsize, char);
         }
-	memcpy(buffer + buflen, bufp, size);
-	buflen += size;
+        while (size-- > 0) {
+            char c = *bufp++;
+            if (sanitise)
+                c = filename_char_sanitise(c);
+            buffer[buflen++] = c;
+        }
     }
     buffer[buflen] = '\0';
 

putty.h

@@ -1305,6 +1305,7 @@ int filename_serialise(const Filename *f, void *data);
 Filename *filename_deserialise(void *data, int maxsize, int *used);
 char *get_username(void);	       /* return value needs freeing */
 char *get_random_data(int bytes);      /* used in cmdgen.c */
+char filename_char_sanitise(char c);   /* rewrite special pathname chars */
 
 /*
  * Exports and imports from timing.c.

unix/uxmisc.c

@@ -94,6 +94,13 @@ Filename *filename_deserialise(void *vdata, int maxsize, int *used)
     return filename_from_str(data);
 }
 
+char filename_char_sanitise(char c)
+{
+    if (c == '/')
+        return '.';
+    return c;
+}
+
 #ifdef DEBUG
 static FILE *debug_fp = NULL;
 

windows/winmisc.c

@@ -69,6 +69,13 @@ Filename *filename_deserialise(void *vdata, int maxsize, int *used)
     return filename_from_str(data);
 }
 
+char filename_char_sanitise(char c)
+{
+    if (strchr("<>:\"/\\|?*", c))
+        return '.';
+    return c;
+}
+
 #ifndef NO_SECUREZEROMEMORY
 /*
  * Windows implementation of smemclr (see misc.c) using SecureZeroMemory.