add filesystem hardening (mounting external filesystems read-only, nosuid, and so on)

[schsh.git] / schsh

diff --git a/schsh b/schsh
index e9464de65dfd0309d025af018be937e9efac1612..823eeaa70cfcf710311451f5ae610dfa0769d888 100755 (executable)
--- a/schsh
+++ b/schsh
@@ -1,16 +1,39 @@
-#!/usr/bin/python
+#!/usr/bin/python3
+import logging, logging.handlers
+import os, sys, shlex, pwd

 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
 # Configuration
 shell = None # set to "/bin/bash" or similar to allow shell access
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
 # Configuration
 shell = None # set to "/bin/bash" or similar to allow shell access

-allowCommands = ["scp", "rsync", "/usr/lib/openssh/sftp-server"]
-commandPaths = ["/usr/bin", "/bin"]
+rrsync = "/usr/local/bin/schsh-rrsync" # path to the restricted rsync script - if available, it will be used to further restrict rsync access
+
+def allowSCP(run, runstr):
+       if len(run) != 3: return False
+       if run[0] != "scp": return False
+       if run[1] not in ("-f", "-t"): return False
+       if run[2].startswith('-'): return False
+       run[0] = "/usr/bin/scp"
+       return True
+
+def allowRSync(run, runstr):
+       if len(run) < 3: return False
+       if run[0] != "rsync": return False
+       if run[1] != "--server": return False
+       if rrsync is None:
+               # rrsync is not available, let's hope this is enough protection
+               run[0] = "/usr/bin/rsync"
+               return True
+       run[:] = [rrsync, "/", runstr] # allow access to the entire chroot
+       return True
+
+def allowSFTP(run, runstr):
+       return runstr == "/usr/lib/openssh/sftp-server"
+
+allowCommands = [allowSCP, allowRSync, allowSFTP]

 
 # END of Configuration
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
 # DO NOT TOUCH ANYTHING BELOW THIS LINE
 
 
 # END of Configuration
 #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
 # DO NOT TOUCH ANYTHING BELOW THIS LINE
 

-import logging, logging.handlers
-import os, sys, shlex, pwd

 
 logger = logging.getLogger("schsh")
 logger.setLevel(logging.INFO)
 
 logger = logging.getLogger("schsh")
 logger.setLevel(logging.INFO)


@@ -27,32 +50,27 @@ def logquit(msg):
        log(msg, logging.ERROR)
        sys.exit(1)
 
        log(msg, logging.ERROR)
        sys.exit(1)
 

-def addPath(prog):
-       if prog.startswith("/"):
-               return prog
-       # look for it in the paths
-       for path in commandPaths:
-               fullprog = os.path.join(path, prog)
-               if os.path.exists(fullprog):
-                       return fullprog
-       return None
+def commandAllowed(run, runstr):
+       for allowed in allowCommands:
+               if allowed(run, runstr):
+                       return True
+       return False

 
 # parse arguments
 run = []
 if len(sys.argv) == 1:
        if shell is None:
 
 # parse arguments
 run = []
 if len(sys.argv) == 1:
        if shell is None:

-               print "No shell for you!"
+               print("No shell for you!")

                logquit("Shell access not allowed")
        else:
                run = [shell]
 elif len(sys.argv) == 3 and sys.argv[1] == "-c":
        # check if the command is allowed, and add path
        run = shlex.split(sys.argv[2])
                logquit("Shell access not allowed")
        else:
                run = [shell]
 elif len(sys.argv) == 3 and sys.argv[1] == "-c":
        # check if the command is allowed, and add path
        run = shlex.split(sys.argv[2])

-       if len(run) > 0 and run[0] in allowCommands:
-               run[0] = addPath(run[0])
+       if commandAllowed(run, sys.argv[2]): # this may change run, but that's okay

                log("Running '"+str(run)+"'")
        else:
                log("Running '"+str(run)+"'")
        else:

-               print "You are not allowed to run this command."
+               print("You are not allowed to run this command.")

                logquit("Attempt to run invalid command '"+sys.argv[2]+"'")
 else:
        logquit("Invalid arguments for schsh: "+str(sys.argv))
                logquit("Attempt to run invalid command '"+sys.argv[2]+"'")
 else:
        logquit("Invalid arguments for schsh: "+str(sys.argv))