Small patch for ftpd to prevent deleting files.

[Aristotelis]

  Hello all,

I was trying to setup a backup server for a number of machines, and for 
a number of reasons ftp was choosen as the underlying tranfer protocol. 
Since in this backup server from a ftp point of view I wanted to make 
the files "immutable", but also i wanted the user to be able to create 
new files under certain directories, i was looking ways to achieve it 
with ftpd.
  I didn't find an obvious solution, so i wrote a small patch that adds 
the -p flag to ftpd and prevents the user from issueing the DELE 
command. (i didn't like much using -p, but i couldn't think of anything 
better).
  Anyhow, i attach the patch, if anyone finds it useful. (flages, 
suggestions, etc also welcomed ;) )

    Best Regards,
     Aristotelis
diff -Naur /usr/src/libexec/ftpd/ftpcmd.y ./ftpd/ftpcmd.y
--- /usr/src/libexec/ftpd/ftpcmd.y      Thu Nov  5 16:43:15 2009
+++ ./ftpd/ftpcmd.y     Tue Nov 10 16:50:04 2009
@@ -82,6 +82,7 @@
 extern int portcheck;
 extern union sockunion his_addr;
 extern int umaskchange;
+extern  int no_dele;
 
 off_t  restart_point;
 
@@ -394,10 +395,16 @@
                }
        | DELE check_login SP pathname CRLF
                {
-                       if ($2 && $4 != NULL)
-                               delete($4);
-                       if ($4 != NULL)
-                               free($4);
+                        if (no_dele) {
+                                reply(550,
+                                    "No permission to delete files");
+                        }
+                        else {
+                                if ($2 && $4 != NULL)
+                                        delete($4);
+                                if ($4 != NULL)
+                                        free($4);
+                        }
                }
        | RNTO check_login SP pathname CRLF
                {
diff -Naur /usr/src/libexec/ftpd/ftpd.c ./ftpd/ftpd.c
--- /usr/src/libexec/ftpd/ftpd.c        Thu Nov  5 16:43:16 2009
+++ ./ftpd/ftpd.c       Tue Nov 10 16:51:13 2009
@@ -154,6 +154,7 @@
 #endif
 mode_t defumask = CMASK;               /* default umask value */
 int    umaskchange = 1;                /* allow user to change umask value. */
+int     no_dele = 0 ;          /* disallow ftp delete */
 char   tmpline[7];
 char   hostname[MAXHOSTNAMELEN];
 char   remotehost[MAXHOSTNAMELEN];
@@ -252,13 +253,13 @@
        return (guest ? path+1 : path);
 }
 
-char *argstr = "AdDhnlMSt:T:u:UvP46";
+char *argstr = "AdDhnlMSt:T:u:UvP46p";
 
 static void
 usage(void)
 {
        syslog(LOG_ERR,
-           "usage: ftpd [-46ADdlMnPSU] [-T maxtimeout] [-t timeout] [-u 
mask]");
+           "usage: ftpd [-46ADdlMnPSUp] [-T maxtimeout] [-t timeout] [-u 
mask]");
        exit(2);
 }
 
@@ -371,7 +372,9 @@
                case '6':
                        family = AF_INET6;
                        break;
-
+                case 'p':
+                        no_dele = 1;
+                        break;
                default:
                        usage();
                        break;