oss-security - Re: CVE-2023-2002: Linux Bluetooth: Unauthorized management command execution

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Date: Sun, 16 Apr 2023 22:57:27 +0200
From: Steffen Nurpmeso <steffen@...oden.eu>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2023-2002: Linux Bluetooth:
 Unauthorized management command execution

Ruihan Li wrote in
 <w7boj4fg4x2o2bjz7a7zkjk4bgxqvqyuxycdqqw2dl3bhanh6a@...tbccffxgv>:
 ...
 |be privileged, such as a setuid program. Moreover, if the socket is used as
 |stdout or stderr, an ioctl call is made to obtain tty parameters, which \
 |can be
 |verified through the strace command.
 |```
 |# strace -e trace=ioctl sudo > /dev/null
 |ioctl(3, TIOCGPGRP, [30305])            = 0
 |ioctl(2, TIOCGWINSZ, {ws_row=45, ws_col=190, ws_xpixel=0, ws_ypixel=0}) = 0
 |```
 ...
 |# find . -user root -perm -4000 -exec sh -c "strace -e trace=ioctl \
 |{} < /dev/null 2>&1 > /dev/null | grep ioctl > /dev/null && echo -n \
 |'V ' || echo -n 'S '; echo {};" \; | sort
 |S ./chage
 |S ./expiry
 |S ./fusermount
 |S ./fusermount3
 |S ./gpasswd
 |S ./ksu
 |S ./mount.cifs
 |S ./sg
 |S ./umount
 |V ./chfn
 |V ./chsh
 |V ./mount
 |V ./newgrp
 |V ./passwd
 |V ./pkexec
 |V ./screen-4.9.0
 |V ./su
 |V ./sudo
 |V ./unix_chkpwd
 |```
 |After manually checking the strace output, it is found that all of \
 |these ioctl
 |users are using ioctl calls on stdin, stdout, or stderr to get or set \
 |some tty
 |parameters. Note that exactly no arguments are passed to these setuid

Your discovered bluetooth bug totally aside.

I wonder -- have you verified that they do not use isatty(3) aka
some tc*() series *first*?  The above with sudo does for example
not reveal anything as shown, roght?  FD 2 seems to be a terminal,
.. and whereas i do not have sudo src here, i am sure it uses
isatty(3) and tcgetattr(3).

I find it hard to believe that people simply use terminal ioctl(2)
etc on file descriptors without verifying that they are, well,
indeed terminal file descriptors?  For example, su(1), as above,
of Linux shadow-utils works a bit, i read for example

       * Be more paranoid, like su from SimplePAMApps.  --marekm

So this general beating onto SETUID or super capable programs
smells like bad fish Hollywood boom-boom again, no?
You have to do some things, and if you give up privileges
thereafter, extended capabilities are gone.
Here locally Xorg now is

  #!/bin/sh
  #
  # Execute Xorg.wrap if it exists otherwise execute Xorg directly.
  # This allows distros to put the suid wrapper in a separate package.

  basedir="/usr/lib/xorg-server"
  if [ -x "$basedir"/Xorg.wrap ]; then
          exec "$basedir"/Xorg.wrap "$@"
  else
          exec "$basedir"/Xorg "$@"
  fi

  $ ll /usr/lib/xorg-server|grep Xorg
  -r-sr-xr-x 1 root root   14632 Mar 31 21:24 Xorg.wrap*
  -rwxr-xr-x 1 root root 2482224 Mar 31 21:24 Xorg*

and so i had to adjust my startx.sh

  X=
  if [ -x /usr/lib/xorg-server/Xorg ]; then
     g=`groups`
     if { echo ${g} | grep -q video; } >/dev/null 2>&1 &&
           { echo ${g} | grep -q input; } >/dev/null 2>&1; then
        X=/usr/lib/xorg-server/Xorg
     fi
     unset g
  fi

  if [ -n "${X}" ]; then
     :
  elif [ -x /usr/lib/xorg-server/Xorg.wrap ]; then
     X=/usr/lib/xorg-server/Xorg.wrap
  elif command -v Xorg; then
     X=Xorg
  else
     X=X
  fi

and furthermore i indeed find myself now in video, input (and
audio) on this box.  What a maintance mess.
(Maintenance is a real thing, i for example have ssh access to
servers where in (/var)?/tmp/ you will find stale temporary files
older than one and a half decade!  Isn't that sheer grazy:

  l#?0|...$ ll /var/tmp/
  Gesamt 874514
  -rw-------   1 dam      ...         8192 Nov 22  2008 Rx_2ay14
  ...
  -rw-------   1 schwarze ...        25232 Aug  6  2016 aaaJTaazJ
  ...

Then something capable that is nicely programmed, saw many eyes,
and looses privileges as soon as possible i prefer.  Hey -- or
make it message passing aware, use TLS connections, marshal via
normalized Unicode and XML, and ask question over an otherwise
under-documented message protocol, that uses totally
under-documented cryptical XML configuration files, and that
somehow gives you resources via a passed-back file descriptor, or
something like this.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)

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