From: Iain Patterson <me@iain.cx>
Date: Wed, 17 Mar 2010 13:28:57 +0000 (+0000)
Subject: Exploit bash POSIXLY_CORRECT mode.
X-Git-Url: http://git.iain.cx/?p=profile.git;a=commitdiff_plain;h=09eb9824be8828dfcd52a679e85007388c098688

Exploit bash POSIXLY_CORRECT mode.

Avoid ugly --rcfile lines in ps output by exploiting the fact that a
POSIX mode bash will read startup commands from the file specified in
ENV.
Set ENV and POSIXLY_CORRECT for startup, unsetting them and disabling
POSIX mode as the first actions in the new shell.
---

diff --git a/opt/bin/became b/opt/bin/became
index 694810d..ca1a523 100755
--- a/opt/bin/became
+++ b/opt/bin/became
@@ -1,8 +1,8 @@
 #!/bin/bash
 
 file="${TMPDIR:-/tmp}/$SUDO_USER.became.$USER.$RANDOM.$$"
-( umask 077; cat > "$file"; echo "/bin/rm -f '$file'" >> "$file" )
-exec </dev/tty /bin/bash --rcfile "$file"
+( umask 077; echo "unset ENV POSIXLY_CORRECT; set +o posix" > "$file"; cat >> "$file"; echo "/bin/rm -f '$file'" >> "$file" )
+exec </dev/tty env ENV="$file" POSIXLY_CORRECT=1 /bin/bash
 # Fall back to the shell.
 exec </dev/tty /bin/bash
 exit 111