Re: [SECURITY] /proc/$pid/ leaks contents across setuid exec

Eric W. Biederman
2011-02-08T20:17:13Z

Kees Cook <kees.cook@canonical.com> writes:

> On Tue, Feb 08, 2011 at 02:43:15PM +1100, James Morris wrote:
>> On Mon, 7 Feb 2011, Kees Cook wrote:
>> > Sure, I know about O_CLOEXEC, but this is about protecting the
>> > just-been-execed setuid process from the attacking process that has no
>> > reason to set O_CLOEXEC.
>> >
>> > Something like this needs to be enforced on the kernel side. I.e. these
>> > file in /proc need to have O_CLOEXEC set in a way that cannot be unset.
>> >
>> > > Changing the behavior in the core kernel will break userspace.
>> >
>> > I don't think /proc/$pid/* needs to stay open across execs, does it? Or at
>> > least the non-0444 files should be handled separately.
>>
>> Actually, this seems like a more general kind of bug in proc rather than a
>> leaked fd. Each child task should only see its own /proc/[pid] data.
>
> Right, that's precisely the problem. The unprivileged process can read
> the setuid process's /proc files.

If these are things that we actually care about we should sprinkle in a
few more ptrace_may_access calls into implementations of the relevant
proc files.

Eric