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From: ebiederm@xmission.com (Eric W. Biederman)
To: Jann Horn <jann@thejh.net>
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: Sun, 30 Oct 2016 23:14:04 -0500	[thread overview]
Message-ID: <87d1ih5f5f.fsf@xmission.com> (raw)
In-Reply-To: <20161030190915.GD2558@pc.thejh.net> (Jann Horn's message of "Sun, 30 Oct 2016 20:09:15 +0100")

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.

Eric


  reply	other threads:[~2016-10-31  4:16 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 [this message]
2016-10-31 13:39         ` Jann Horn
2016-11-03 20:43         ` Krister Johansen

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