On Fri, May 10, 2019 at 1:41 PM Jann Horn [off-list ref] wrote:

On Tue, May 07, 2019 at 05:17:35AM +1000, Aleksa Sarai wrote:

quoted

On 2019-05-06, Jann Horn [off-list ref] wrote:

quoted

In my opinion, CVE-2019-5736 points out two different problems:

The big problem: The __ptrace_may_access() logic has a special-case
short-circuit for "introspection" that you can't opt out of; this
makes it possible to open things in procfs that are related to the
current process even if the credentials of the process wouldn't permit
accessing another process like it. I think the proper fix to deal with
this would be to add a prctl() flag for "set whether introspection is
allowed for this process", and if userspace has manually un-set that
flag, any introspection special-case logic would be skipped.

We could do PR_SET_DUMPABLE=3 for this, I guess?

Hmm... I'd make it a new prctl() command, since introspection is
somewhat orthogonal to dumpability. Also, dumpability is per-mm, and I
think the introspection flag should be per-thread.

I've lost track of the context here, but it seems to me that
mitigating attacks involving accidental following of /proc links
shouldn't depend on dumpability.  What's the actual problem this is
trying to solve again?