From: Jann Horn <jann@thejh.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Krister Johansen <kjlx@templeofstupid.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Roland McGrath <roland@hack.frob.com>,
Oleg Nesterov <oleg@redhat.com>,
John Johansen <john.johansen@canonical.com>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
Paul Moore <aul@paul-moore.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
Eric Paris <eparis@parisplace.org>,
Casey Schaufler <casey@schaufler-ca.com>,
Kees Cook <keescook@chromium.org>,
Andrew Morton <akpm@linux-foundation.org>,
Janis Danisevskis <jdanis@google.com>,
Seth Forshee <seth.forshee@canonical.com>,
Thomas Gleixner <tglx@linutronix.de>,
Benjamin LaHaise <bcrl@kvack.org>,
Ben Hutchings <ben@decadent.org.uk>,
Andy Lutomirski <luto@amacapital.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, security@kernel.org
Subject: Re: [PATCH v2 8/8] Documentation: add security/ptrace_checks.txt
Date: Mon, 31 Oct 2016 14:39:20 +0100 [thread overview]
Message-ID: <20161031133919.GB2836@pc.thejh.net> (raw)
In-Reply-To: <87d1ih5f5f.fsf@xmission.com>
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On Sun, Oct 30, 2016 at 11:14:04PM -0500, Eric W. Biederman wrote:
> Jann Horn <jann@thejh.net> writes:
>
> > On Sat, Oct 01, 2016 at 08:16:00PM -0700, Krister Johansen wrote:
> >> On Fri, Sep 23, 2016 at 10:40:38PM +0200, Jann Horn wrote:
> >> > +=====================
> >> > +FILESYSTEM DEBUG APIS
> >> > +=====================
> >> > +
> >> > +The pid / tgid entries in procfs contain various entries that allow debugging
> >> > +access to a process. Interesting entries are:
> >> > +
> >> > + - auxv permits an ASLR bypass
> >> > + - cwd can permit bypassing filesystem restrictions in some cases
> >> > + - environ can leak secret tokens
> >> > + - fd can permit bypassing filesystem restrictions or leak access to things like
> >> > + pipes
> >> > + - maps permits an ASLR bypass
> >> > + - mem grants R+W access to process memory
> >> > + - stat permits an ASLR bypass
> >> > +
> >> > +Of these, all use both a normal filesystem DAC check (where the file owner is
> >> > +the process owner for a dumpable process, root for a nondumpable process) and a
> >> > +ptrace_may_access() check; however, the DAC check may be modified, and the
> >> > +ptrace_may_access() is performed under PTRACE_FSCREDS, meaning that instead of
> >> > +the caller's ruid, rgid and permitted capabilities, the fsuid, fsgid and
> >> > +effective capabilities are used, causing the case where a daemon drops its euid
> >> > +prior to accessing a file for the user to be treated correctly for this check.
> >>
> >> Thanks for writing this up.
> >>
> >> Is it worth mentioning some of the less obvious aspects of how user
> >> namespaces interact with the filesystem debug APIs? Of particular note:
> >> a nondumpable process will always be assigned the global root ids.
> >> Checks against capabilities for procfs require that the uid and gid have
> >> a mapping in the current namepsace. That's enforced through
> >> capable_wrt_inode_uidgid().
> >
> > Yeah, makes sense. Added that. Thanks!
>
> That will actually be changing for 4.10. mm->user_ns allows me to use
> the user namespace id 0 if that id is mapped.
Okay, I'll take it back out for now.
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next prev parent reply other threads:[~2016-10-31 13:39 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-23 20:40 [PATCH v2 0/8] Various fixes related to ptrace_may_access() Jann Horn
2016-09-23 20:40 ` [PATCH v2 1/8] exec: introduce cred_guard_light Jann Horn
2016-09-30 15:35 ` Oleg Nesterov
2016-09-30 18:27 ` Eric W. Biederman
2016-10-03 16:02 ` Oleg Nesterov
2016-10-30 21:12 ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 2/8] exec: turn self_exec_id into self_privunit Jann Horn
2016-09-23 21:04 ` Andy Lutomirski
2016-09-23 21:33 ` Jann Horn
2016-09-30 13:20 ` Oleg Nesterov
2016-09-30 13:44 ` Oleg Nesterov
2016-09-30 18:30 ` Kees Cook
2016-09-30 18:59 ` Jann Horn
2016-09-30 19:05 ` Kees Cook
2016-10-03 16:37 ` Oleg Nesterov
2016-09-23 20:40 ` [PATCH v2 3/8] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-23 20:40 ` [PATCH v2 4/8] futex: don't leak robust_list pointer Jann Horn
2016-09-30 14:52 ` Oleg Nesterov
2016-10-30 17:16 ` Jann Horn
2016-11-02 21:39 ` Jann Horn
2016-11-02 22:47 ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 5/8] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-23 20:40 ` [PATCH v2 6/8] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-23 20:40 ` [PATCH v2 7/8] fs/proc: fix attr access check Jann Horn
2016-09-23 20:40 ` [PATCH v2 8/8] Documentation: add security/ptrace_checks.txt Jann Horn
2016-10-02 3:16 ` Krister Johansen
2016-10-30 19:09 ` Jann Horn
2016-10-31 4:14 ` Eric W. Biederman
2016-10-31 13:39 ` Jann Horn [this message]
2016-11-03 20:43 ` Krister Johansen
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