> On May 3, 2023, at 6:53 AM, Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx> wrote:
>
> Hi Christian,
>
> On 03/05/23 12:30 pm, Christian Brauner wrote:
>> On Tue, May 02, 2023 at 06:23:51PM +0000, Chuck Lever III wrote:
>>>
>>>
>>>> On May 2, 2023, at 12:50 PM, Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote:
>>>>
>>>>
>>>>
>>>>> On May 2, 2023, at 9:49 AM, Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote:
>>>>>
>>>>>>
>>>>>> On May 2, 2023, at 9:36 AM, Christian Brauner <brauner@xxxxxxxxxx> wrote:
>>>>>>
>>>>>> We've aligned setgid behavior over multiple kernel releases. The details
>>>>>> 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 bit 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 retain the
>>>>>> setgid bit.
>>>>>>
>>>>>> Without this patch the setgid stripping tests in LTP will fail:
>>>>>>
>>>>>>> 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
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> fchown02.c:66: TFAIL: testfile2: wrong mode permissions 0100700, expected 0102700
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> chown02.c:57: TFAIL: testfile2: wrong mode permissions 0100700, expected 0102700
>>>>>>
>>>>>> With this patch all tests pass.
>>>>>>
>>>>>> Reported-by: Sherry Yang <sherry.yang@xxxxxxxxxx>
>>>>>> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
>>>>>
>
> We had a very similar report from kernel-test-robot.
>
> https://lore.kernel.org/all/202210091600.dbe52cbf-yujie.liu@xxxxxxxxx/
>
> Which points to commit: ed5a7047d201 ("attr: use consistent sgid stripping checks")
>
> And the above commit is backported to LTS kernels -- 5.10.y,5.15.y and 6.1.y
>
> So would it be better to tag it to stable by adding "Cc: <stable@xxxxxxxxxxxxxxx>" ?
>
> Thanks,
> Harshit
>
>>>>> There are some similar fstests failures this fix might address.
>>>>>
>>>>> I've applied this patch to the nfsd-fixes tree for broader
>>>>> testing.
>>>>
>>>> ERROR: modpost: "setattr_should_drop_sgid" [fs/nfsd/nfsd.ko] undefined!
>>>>
>>>> Did I apply this patch to the wrong kernel?
>>>
>>> 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
I'll apply this to nfsd-next (6.5) and add Jeff's Reviewed-by
and a Cc: stable.
--
Chuck Lever
