Problem with exec shell_escape option

21 Dec 2016

      I'm trying to get exec to pass a string as an argument without any shell 
quoting, but not succeeding. This is with freeradius 3.0.12 under Ubuntu 
16.04.

[Aside: what I'm actually trying to do is invoke an external change 
password program using an exec expansion in local_cpw in rlm_mschap, 
following the example given:

#        local_cpw = "%{exec:/path/to/script %{mschap:User-Name} 
%{MS-CHAP-New-Cleartext-Password}}"

But I'm finding that passwords with special characters are being mangled]

I can reproduce this using exec by itself. Here are 4 combinations: 
shell_escape = {yes,no} and expansion argument quoted/not quoted.

# mods-available/exec - I left the original exec in there and added:

exec exec1 {
     wait = yes
     input_pairs = request
     shell_escape = no
     timeout = 10
}
exec exec2 {
     wait = yes
     input_pairs = request
     shell_escape = yes
     timeout = 10
}

# policy.d/testpolicy

testpolicy {
   update request {
     &Tmp-String-0 := " foo ' bar \" baz \\ qux "
     &Tmp-String-1 := "%{exec1:/usr/local/bin/showarg %{Tmp-String-0}}"
     &Tmp-String-2 := "%{exec1:/usr/local/bin/showarg '%{Tmp-String-0}'}"
     &Tmp-String-3 := "%{exec2:/usr/local/bin/showarg %{Tmp-String-0}}"
     &Tmp-String-4 := "%{exec2:/usr/local/bin/showarg '%{Tmp-String-0}'}"
   }
}

# /usr/local/bin/showarg

#!/bin/sh
echo "Arg is <$1>" >>/tmp/exec.log

Results:

- 1 and 3 fail with "rad_expand_xlat: Invalid string passed as argument"

- 2 and 4 both apply shell quoting to the argument

# cat /tmp/exec.log
Arg is <\ foo\ \'\ bar\ "\ baz\ \ qux\ >
Arg is <\ foo\ \'\ bar\ "\ baz\ \ qux\ >

Debug output:

(0)     policy testpolicy {
(0)       update request {
(0)         &Tmp-String-0 := " foo ' bar \" baz \\ qux "
(0)         Executing: /usr/local/bin/showarg \ foo\ \'\ bar\ "\ baz\ \\ 
qux\ :
rad_expand_xlat: Invalid string passed as argument
invalid command line '/usr/local/bin/showarg \ foo\ \'\ bar\ "\ baz\ \\ 
qux\ '.
(0)         EXPAND %{exec1:/usr/local/bin/showarg %{Tmp-String-0}}
(0)            -->
(0)         &Tmp-String-1 :=
(0)         Executing: /usr/local/bin/showarg '\ foo\ \'\ bar\ "\ baz\ 
\\ qux\ ':
(0)         Program returned code (0) and output ''
(0)         EXPAND %{exec1:/usr/local/bin/showarg '%{Tmp-String-0}'}
(0)            -->
(0)         &Tmp-String-2 :=
(0)         Executing: /usr/local/bin/showarg \ foo\ \'\ bar\ "\ baz\ \\ 
qux\ :
rad_expand_xlat: Invalid string passed as argument
invalid command line '/usr/local/bin/showarg \ foo\ \'\ bar\ "\ baz\ \\ 
qux\ '.
(0)         EXPAND %{exec2:/usr/local/bin/showarg %{Tmp-String-0}}
(0)            -->
(0)         &Tmp-String-3 :=
(0)         Executing: /usr/local/bin/showarg '\ foo\ \'\ bar\ "\ baz\ 
\\ qux\ ':
(0)         Program returned code (0) and output ''
(0)         EXPAND %{exec2:/usr/local/bin/showarg '%{Tmp-String-0}'}
(0)            -->
(0)         &Tmp-String-4 :=
(0)       } # update request = noop
(0)     } # policy testpolicy = noop

So it looks like the shell_escape setting isn't doing anything. What am 
I missing?

Thanks,

Brian.

P.S. There is something else confusing. In raddb/mods-available/exec it 
says:

#  Execute external programs
#
#  This module is useful only for 'xlat'.  To use it,
#  put 'exec' into the 'instantiate' section.  You can then
#  do dynamic translation of attributes like:
#
#  Attribute-Name = `%{exec:/path/to/program args}`

However, I can see from the source that it has hooks for the various 
module lifecycle stages; indeed, the sites-available/default config 
invokes it in the accounting and post-auth stages:

         # For Exec-Program and Exec-Program-Wait
         exec

So is the comment that exec is "useful only for 'xlat'" incorrect?

I've checked the obvious places for documentation with no luck:

- http://wiki.freeradius.org/search?q=exec
- man rlm_exec  (not found)

But in any case, it doesn't affect the main issue here, since local_cpw 
has to use a string expansion anyway.

Problem with exec shell_escape option

Brian Candler