linux-kernel - Re: [PATCH] ptrace: being capable wrt a process requires mapped uids/gids

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Date:	Sat, 26 Dec 2015 18:03:00 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Cc:	Jann Horn <jann@...jh.net>, Roland McGrath <roland@...k.frob.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"security@...nel.org" <security@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] ptrace: being capable wrt a process requires mapped uids/gids

On Sat, Dec 26, 2015 at 1:51 PM, Serge E. Hallyn
<serge.hallyn@...ntu.com> wrote:
> On Sat, Dec 26, 2015 at 03:52:31AM +0100, Jann Horn wrote:
>> ptrace_has_cap() checks whether the current process should be
>> treated as having a certain capability for ptrace checks
>> against another process. Until now, this was equivalent to
>> has_ns_capability(current, target_ns, CAP_SYS_PTRACE).
>>
>> However, if a root-owned process wants to enter a user
>> namespace for some reason without knowing who owns it and
>> therefore can't change to the namespace owner's uid and gid
>> before entering, as soon as it has entered the namespace,
>> the namespace owner can attach to it via ptrace and thereby
>> gain access to its uid and gid.
>>
>> While it is possible for the entering process to switch to
>> the uid of a claimed namespace owner before entering,
>> causing the attempt to enter to fail if the claimed uid is
>> wrong, this doesn't solve the problem of determining an
>> appropriate gid.
>>
>> With this change, the entering process can first enter the
>> namespace and then safely inspect the namespace's
>> properties, e.g. through /proc/self/{uid_map,gid_map},
>> assuming that the namespace owner doesn't have access to
>> uid 0.
>>
>> Changed in v2: The caller needs to be capable in the
>> namespace into which tcred's uids/gids can be mapped.
>>
>> Signed-off-by: Jann Horn <jann@...jh.net>
>
> Acked-by: Serge Hallyn <serge.hallyn@...ntu.com>

Acked-by: Andy Lutomirski <luto@...nel.org>

Who's going to apply this?  Linus?  Eric?

--Andy
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