Your issue has to do with permission inheritance.
cdbootstrap will inherit the permissions of
fakeroot, which can be elevated via
sudo fakeroot cdbootstrap /tmp/foo
If the above command succeeds, permissions on
/tmp are the issue. See What are common rights for /tmp ? I unintentionnally set it all public recursively, for what the default permissions should be. Generally, writing anything into
/tmp that wasn't put there by an application is a bad idea, and
fakeroot has it's own issues. From the man page:
Every command executed within fakeroot needs to be linked to the
same version of the C library as fakeroot itself.
fakeroot doesn't wrap open(), create(), etc. So, if user joost
ls -al foo
or the other way around,
ls -al foo
fakeroot has no way of knowing that in the first case, the owner
of foo really should be joost while the second case it should
have been root. For the Debian packaging, defaulting to giving
all "unknown" files uid=gid=0, is always OK. The real way around
this is to wrap open() and create(), but that creates other
problems, as demonstrated by the libtricks package. This package
wrapped many more functions, and tried to do a lot more than
fakeroot . It turned out that a minor upgrade of libc (from one
where the stat() function didn't use open() to one with a stat()
function that did (in some cases) use open()), would cause unex-
plainable segfaults (that is, the libc6 stat() called the
wrapped open(), which would then call the libc6 stat(), etc).
Fixing them wasn't all that easy, but once fixed, it was just a
matter of time before another function started to use open(),
never mind trying to port it to a different operating system.
Thus I decided to keep the number of functions wrapped by fake-
root as small as possible, to limit the likelihood of 'colli-
GNU configure (and other such programs)
of the file will be 000. The bug is that if root does the same, open()
will succeed, as the file permissions aren't checked at all for root. I
choose not to wrap open(), as open() is used by many other functions in
libc (also those that are already wrapped), thus creating loops (or
possible future loops, when the implementation of various libc func-
tions slightly change).
Instead of using privilege escalation to achieve what you're trying to do consider using a proper
chroot, as outlined in the DebootstrapChroot Documentation for Ubuntu, or the Official Debian Documentation for DebBootStrap.