linux-kernel - Re: [PATCH v4 3/3] binder: use euid from cred instead of using task

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Message-ID: <6dd3cdff-c4eb-6457-f04c-199263acd80b@schaufler-ca.com>
Date:   Fri, 8 Oct 2021 14:25:39 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Paul Moore <paul@...l-moore.com>, Todd Kjos <tkjos@...gle.com>
Cc:     gregkh@...uxfoundation.org, arve@...roid.com, tkjos@...roid.com,
        maco@...roid.com, christian@...uner.io,
        James Morris <jmorris@...ei.org>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, keescook@...omium.org,
        jannh@...gle.com, Jeffrey Vander Stoep <jeffv@...gle.com>,
        zohar@...ux.ibm.com, linux-security-module@...r.kernel.org,
        selinux@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, joel@...lfernandes.org,
        kernel-team@...roid.com, stable@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v4 3/3] binder: use euid from cred instead of using task

On 10/8/2021 2:12 PM, Paul Moore wrote:
> On Wed, Oct 6, 2021 at 8:46 PM Todd Kjos <tkjos@...gle.com> wrote:
>> Set a transaction's sender_euid from the 'struct cred'
>> saved at binder_open() instead of looking up the euid
>> from the binder proc's 'struct task'. This ensures
>> the euid is associated with the security context that
>> of the task that opened binder.
>>
>> Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
>> Signed-off-by: Todd Kjos <tkjos@...gle.com>
>> Suggested-by: Stephen Smalley <stephen.smalley.work@...il.com>
>> Cc: stable@...r.kernel.org # 4.4+
>> ---
>> v3: added this patch to series
>>
>>  drivers/android/binder.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
> This is an interesting ordering of the patches.  Unless I'm missing
> something I would have expected patch 3/3 to come first, followed by
> 2/3, with patch 1/3 at the end; basically the reverse of what was
> posted here.
>
> My reading of the previous thread was that Casey has made his peace
> with these changes

Yes. I will address the stacking concerns more directly.
I am still somewhat baffled by the intent of the hook, the data
passed to it, and the SELinux policy enforcement decisions, but
that's beyond my scope.

>  so unless anyone has any objections I'll plan on
> merging 2/3 and 3/3 into selinux/stable-5.15 and merging 1/3 into
> selinux/next.
>
>> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
>> index 989afd0804ca..26382e982c5e 100644
>> --- a/drivers/android/binder.c
>> +++ b/drivers/android/binder.c
>> @@ -2711,7 +2711,7 @@ static void binder_transaction(struct binder_proc *proc,
>>                 t->from = thread;
>>         else
>>                 t->from = NULL;
>> -       t->sender_euid = task_euid(proc->tsk);
>> +       t->sender_euid = proc->cred->euid;
>>         t->to_proc = target_proc;
>>         t->to_thread = target_thread;
>>         t->code = tr->code;
>> --
>> 2.33.0.800.g4c38ced690-goog
> --
> paul moore
> www.paul-moore.com