[rqd] Check if uid is valid before launching frame (#1661)

If the frame uid is outside of linux defined UID_MAX and UID_MIN
fallback to the uid of the daemon user. Read
https://www.man7.org/linux/man-pages/man5/login.defs.5.html for more
information about uid limits. At this time, limits are hardcoded on
rqconstants as the linux default values, which sounds reasonable as this
default config limit is rarely modified.

---------

Signed-off-by: Diego Tavares <[email protected]>
Co-authored-by: Ramon Figueiredo <[email protected]>

rqd/rqd/rqconstants.py

@@ -85,9 +85,14 @@
 if platform.system() == 'Linux':
     RQD_UID = pwd.getpwnam("daemon")[2]
     RQD_GID = pwd.getpwnam("daemon")[3]
+    # Linux's default uid limits are documented at
+    #  https://www.man7.org/linux/man-pages/man5/login.defs.5.html
+    RQD_MIN_UID = 1000
+    RQD_MAX_UID = 60000
 else:
     RQD_UID = 0
     RQD_GID = 0
+RQD_DAEMON_UID = RQD_UID
 
 # Nimby behavior:
 # Number of seconds to wait before checking if the user has become idle.

rqd/rqd/rqcore.py

@@ -1042,14 +1042,20 @@ def runDocker(self):
         self._tempLocations.append(tempStatFile)
 
         # Prevent frame from attempting to run as ROOT
+        gid = runFrame.gid
         if runFrame.gid <= 0:
             gid = rqd.rqconstants.LAUNCH_FRAME_USER_GID
-        else:
-            gid = runFrame.gid
+
+        # Prevent invalid uids, fallback to daemon uid
+        uid = runFrame.uid
+        if uid < rqd.rqconstants.RQD_MIN_UID or uid > rqd.rqconstants.RQD_MAX_UID:
+            msg = "Frame launched with an invalid uid=%s. Falling back to daemon uid" % runFrame.uid
+            self.rqlog.write(msg, prependTimestamp=rqd.rqconstants.RQD_PREPEND_TIMESTAMP)
+            uid = rqd.rqconstants.RQD_DAEMON_UID
 
         # Never give frame ROOT permissions
-        if runFrame.uid == 0 or gid == 0:
-            msg = ("Frame %s cannot run as ROOT" % frameInfo.frameId)
+        if uid == 0 or gid == 0:
+            msg = "Frame %s cannot run as ROOT" % frameInfo.frameId
             self.rqlog.write(msg, prependTimestamp=rqd.rqconstants.RQD_PREPEND_TIMESTAMP)
             raise RuntimeError(msg)
 
@@ -1067,7 +1073,7 @@ def runDocker(self):
 useradd -u %s -g %s -p %s %s >& /dev/null || true;
 exec su -s %s %s -c "echo \$$; /bin/nice /usr/bin/time -p -o %s %s %s"
 """ % (
-            runFrame.uid,
+            uid,
             gid,
             tempPassword,
             runFrame.user_name,