restrict who can setxattr the pseudo file. closes #64

src/getattr.cpp

@@ -48,10 +48,10 @@ _getattr_controlfile(struct stat &buf)
 
   buf.st_dev     = 0;
   buf.st_ino     = 0;
-  buf.st_mode    = (S_IFREG|S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);
+  buf.st_mode    = (S_IFREG|S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH);
   buf.st_nlink   = 1;
-  buf.st_uid     = ::geteuid();
-  buf.st_gid     = ::getegid();
+  buf.st_uid     = ::getuid();
+  buf.st_gid     = ::getgid();
   buf.st_rdev    = 0;
   buf.st_size    = 0;
   buf.st_blksize = 1024;

src/setxattr.cpp

@@ -283,15 +283,20 @@ namespace mergerfs
              int         flags)
     {
       const config::Config      &config = config::get();
+      const struct fuse_context *fc     = fuse_get_context();
 
       if(fusepath == config.controlfile)
+        {
+          if((fc->uid != ::getuid()) && (fc->gid != ::getgid()))
+            return -EPERM;
+
           return _setxattr_controlfile(config::get_writable(),
                                        attrname,
                                        string(attrval,attrvalsize),
                                        flags);
+        }
 
       {
-        const struct fuse_context *fc = fuse_get_context();
         const ugid::SetResetGuard ugid(fc->uid,fc->gid);
         const rwlock::ReadGuard   readlock(&config.srcmountslock);