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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Sherry Yang <sherry.yang@oracle.com>
CC:     Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>,
        Christian Brauner <brauner@kernel.org>,
        Jeff Layton <jlayton@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Darren Kenny <darren.kenny@oracle.com>
Subject: Re: [PATCH] nfsd: use vfs setgid helper
Thread-Topic: [PATCH] nfsd: use vfs setgid helper
Thread-Index: AQHZfPsU0hWi9leffEW/mcTC+uI3U69G/7aAgAAykoCAABoxAIAA02kAgABBLwCAADWlAIATBXuAgAAHlgA=
Date:   Mon, 15 May 2023 17:01:30 +0000
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> On May 15, 2023, at 12:34 PM, Sherry Yang <sherry.yang@oracle.com> wrote:
>=20
>=20
>=20
>> On May 3, 2023, at 7:05 AM, Chuck Lever III <chuck.lever@oracle.com> wro=
te:
>>=20
>>=20
>>=20
>>> On May 3, 2023, at 6:53 AM, Harshit Mogalapalli <harshit.m.mogalapalli@=
oracle.com> wrote:
>>>=20
>>> Hi Christian,
>>>=20
>>> On 03/05/23 12:30 pm, Christian Brauner wrote:
>>>> On Tue, May 02, 2023 at 06:23:51PM +0000, Chuck Lever III wrote:
>>>>>=20
>>>>>=20
>>>>>> On May 2, 2023, at 12:50 PM, Chuck Lever III <chuck.lever@oracle.com=
> wrote:
>>>>>>=20
>>>>>>=20
>>>>>>=20
>>>>>>> On May 2, 2023, at 9:49 AM, Chuck Lever III <chuck.lever@oracle.com=
> wrote:
>>>>>>>=20
>>>>>>>>=20
>>>>>>>> On May 2, 2023, at 9:36 AM, Christian Brauner <brauner@kernel.org>=
 wrote:
>>>>>>>>=20
>>>>>>>> We've aligned setgid behavior over multiple kernel releases. The d=
etails
>>>>>>>> can be found in commit cf619f891971 ("Merge tag 'fs.ovl.setgid.v6.=
2' of
>>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/vfs/idmapping") and
>>>>>>>> commit 426b4ca2d6a5 ("Merge tag 'fs.setgid.v6.0' of
>>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux").
>>>>>>>> Consistent setgid stripping behavior is now encapsulated in the
>>>>>>>> setattr_should_drop_sgid() helper which is used by all filesystems=
 that
>>>>>>>> strip setgid bits outside of vfs proper. Usually ATTR_KILL_SGID is
>>>>>>>> raised in e.g., chown_common() and is subject to the
>>>>>>>> setattr_should_drop_sgid() check to determine whether the setgid b=
it can
>>>>>>>> be retained. Since nfsd is raising ATTR_KILL_SGID unconditionally =
it
>>>>>>>> will cause notify_change() to strip it even if the caller had the
>>>>>>>> necessary privileges to retain it. Ensure that nfsd only raises
>>>>>>>> ATR_KILL_SGID if the caller lacks the necessary privileges to reta=
in the
>>>>>>>> setgid bit.
>>>>>>>>=20
>>>>>>>> Without this patch the setgid stripping tests in LTP will fail:
>>>>>>>>=20
>>>>>>>>> As you can see, the problem is S_ISGID (0002000) was dropped on a
>>>>>>>>> non-group-executable file while chown was invoked by super-user, =
while
>>>>>>>>=20
>>>>>>>> [...]
>>>>>>>>=20
>>>>>>>>> fchown02.c:66: TFAIL: testfile2: wrong mode permissions 0100700, =
expected 0102700
>>>>>>>>=20
>>>>>>>> [...]
>>>>>>>>=20
>>>>>>>>> chown02.c:57: TFAIL: testfile2: wrong mode permissions 0100700, e=
xpected 0102700
>>>>>>>>=20
>>>>>>>> With this patch all tests pass.
>>>>>>>>=20
>>>>>>>> Reported-by: Sherry Yang <sherry.yang@oracle.com>
>>>>>>>> Signed-off-by: Christian Brauner <brauner@kernel.org>
>>>>>>>=20
>>>=20
>>> We had a very similar report from kernel-test-robot.
>>>=20
>>> https://lore.kernel.org/all/202210091600.dbe52cbf-yujie.liu@intel.com/
>>>=20
>>> Which points to commit: ed5a7047d201 ("attr: use consistent sgid stripp=
ing checks")
>>>=20
>>> And the above commit is backported to LTS kernels -- 5.10.y,5.15.y and =
6.1.y
>>>=20
>>> So would it be better to tag it to stable by adding "Cc: <stable@vger.k=
ernel.org>" ?
>>>=20
>>> Thanks,
>>> Harshit
>>>=20
>>>>>>> There are some similar fstests failures this fix might address.
>>>>>>>=20
>>>>>>> I've applied this patch to the nfsd-fixes tree for broader
>>>>>>> testing.
>>>>>>=20
>>>>>> ERROR: modpost: "setattr_should_drop_sgid" [fs/nfsd/nfsd.ko] undefin=
ed!
>>>>>>=20
>>>>>> Did I apply this patch to the wrong kernel?
>>>>>=20
>>>>> setattr_should_drop_sgid() is not available to callers built as
>>>>> modules. It needs an EXPORT_SYMBOL or _GPL.
>>>> Hey Chuck,
>>>> Thanks for taking a look!
>>>> The required export is part of
>>>> commit 4f704d9a835 ("nfs: use vfs setgid helper")
>>>> which is in current mainline as of Monday this week which was part of =
my
>>>> v6.4/vfs.misc PR that was merged.
>>>> So this should all work fine on mainline. Seems I didn't use --base
>>>> which is why that info was missing.
>>>> Thanks!
>>>> Christian
>>=20
>> I'll apply this to nfsd-next (6.5) and add Jeff's Reviewed-by
>> and a Cc: stable.
>=20
> Hi Chuck,
>=20
> Just following up to see if you know when this patch will go to linux mai=
nline and linux-stable?

Howdy- mentioned above: applied to nfsd-next for the v6.5 merge
window, which will open in several weeks.

I added a Cc: stable, so once it is in 6.5-rc it will be automatically
backported into the stable kernels.


--
Chuck Lever