From: ebiederm@xmission.com (Eric W. Biederman)
To: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
        Shuah Khan <shuahkh@osg.samsung.com>, Greg KH <greg@kroah.com>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        "open list\:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Shuah Khan <shuah@kernel.org>
References: <CA+G9fYtpFW+SHcaWCgt5ZAvPx3PO3x3nM+oRBUiOiQPbHVmw=w@mail.gmail.com>
        <20170627151359.GA11756@kroah.com> <20170627151600.GB11756@kroah.com>
        <df3c647e-1724-bcbb-4467-22af0c3be6e7@osg.samsung.com>
        <CAGXu5jKhpCsCZ-4xUyYnBzmAQCi4=CnJKW5daqhZZMZRs-kkwg@mail.gmail.com>
        <CALCETrVJYwoLT6=kQx9fRXzv7eVvC6dBiSHowjHHRrDCDFGJ1A@mail.gmail.com>
        <87fuei6gdu.fsf@xmission.com>
Date: Thu, 29 Jun 2017 09:23:15 -0500
In-Reply-To: <87fuei6gdu.fsf@xmission.com> (Eric W. Biederman's message of
        "Thu, 29 Jun 2017 09:02:53 -0500")
Message-ID: <878tka6ffw.fsf@xmission.com>
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Subject: Re: selftests/capabilities: test FAIL on linux mainline and linux-next and PASS on linux-4.4.70+
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ebiederm@xmission.com (Eric W. Biederman) writes:

> Andy Lutomirski <luto@kernel.org> writes:
>>
>> Hi Eric-
>>
>> This is rather odd.  The selftest
>> (tools/testing/selftests/capabilities/test_execve), run as root, fails
>> on current kernels.  The failure is worked around by this:
>>
>> diff --git a/tools/testing/selftests/capabilities/test_execve.c
>> b/tools/testing/selftests/capabilities/test_execve.c
>> index 10a21a958aaf..6db60889b211 100644
>> --- a/tools/testing/selftests/capabilities/test_execve.c
>> +++ b/tools/testing/selftests/capabilities/test_execve.c
>> @@ -139,8 +139,8 @@ static void chdir_to_tmpfs(void)
>>         if (chdir(cwd) != 0)
>>                 err(1, "chdir to private tmpfs");
>>
>> -       if (umount2(".", MNT_DETACH) != 0)
>> -               err(1, "detach private tmpfs");
>> +//     if (umount2(".", MNT_DETACH) != 0)
>> +//             err(1, "detach private tmpfs");
>>  }
>>
>>  static void copy_fromat_to(int fromfd, const char *fromname, const
>> char *toname)
>>
>> I think this is due to the line:
>>
>> p->mnt_ns = NULL;
>>
>> in umount_tree().  The test is putting us into a situation in which
>> our cwd has ->mnt_ns = NULL, which is making it act as if it's nosuid.
>> I can imagine this breaking some weird user code (like my test!).  Is
>> it a real problem, though?

I just wanted to follow up and say this the mnt_may_suid test appears
to be doing exactly what it was designed to do.

It's goal is not to allow a suid exec from another mount namespace and
in this test the umount2(".", MNT_DETACH) creates a poor man's mount
namespace.

So assuming that we want to not allow execing executables from other
mount namespaces the behavior appears to be exactly correct in this
case.

Eric