linux-kernel - Re: [PATCH] proc: Track /proc/$pid/attr/ opener mm

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Message-ID: <17222cd4-3c2b-9d0c-aa51-64b7a50a9c2c@schaufler-ca.com>
Date:   Mon, 14 Jun 2021 10:52:48 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Kees Cook <keescook@...omium.org>,
        youling257 <youling257@...il.com>
Cc:     torvalds@...ux-foundation.org, christian.brauner@...ntu.com,
        andrea.righi@...onical.com, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, regressions@...ts.linux.dev,
        linux-security-module@...r.kernel.org,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        SElinux list <selinux@...r.kernel.org>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] proc: Track /proc/$pid/attr/ opener mm_struct

On 6/14/2021 8:32 AM, Kees Cook wrote:
> On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
>> I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
>>
>> 06-14 02:15:51.165  1685  1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
>> 06-14 02:15:51.166  1685  1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
>> 06-14 02:15:51.166  1682  1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?).  Retrying...
>> 06-14 02:15:51.197  1685  1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
>> 06-14 02:15:51.197  1685  1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
>> 06-14 02:15:51.198  1695  1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?).  Retrying...
>> 06-14 02:15:51.207  1685  1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
>> 06-14 02:15:51.207  1685  1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
>> 06-14 02:15:51.207  1708  1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?).  Retrying...
>> 06-14 02:15:51.275  1685  1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
>> 06-14 02:15:51.275  1692  1692 I cameraserver: ServiceManager: 0xf6d309e0
>> 06-14 02:15:51.275  1685  1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
>> 06-14 02:15:51.276  1693  1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?).  Retrying...
>>
> Argh. Are you able to uncover what userspace is doing here?
>
> So far, my test cases are:
>
> 1) self: open, write, close: allowed
> 2) self: open, clone thread. thread: change privileges, write, close: allowed
> 3) self: open, give to privileged process. privileged process: write: reject

I found an issue under Smack where a privileged process opened
/proc/self/attr/smack/current, wrote to it successfully, then tried
to write to it again, which failed because the cred has changed. 
That's not a common use case. The usual case is open, write, close.
If ServiceManager is assuming that it can leave a descriptor open
while manipulations are in progress it could encounter the same kind
of problem.