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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Christian Brauner <brauner@kernel.org>
CC:     Jeff Layton <jlayton@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Sherry Yang <sherry.yang@oracle.com>
Subject: Re: [PATCH] nfsd: use vfs setgid helper
Thread-Topic: [PATCH] nfsd: use vfs setgid helper
Thread-Index: AQHZfPsU0hWi9leffEW/mcTC+uI3U69G/7aAgAAykoA=
Date:   Tue, 2 May 2023 16:50:05 +0000
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> On May 2, 2023, at 9:49 AM, Chuck Lever III <chuck.lever@oracle.com> wrot=
e:
>=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 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.
>>=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, expect=
ed 0102700
>>=20
>> [...]
>>=20
>>> chown02.c:57: TFAIL: testfile2: wrong mode permissions 0100700, expecte=
d 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
> There are some similar fstests failures this fix might address.
>=20
> 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?


> Thanks, Christian and Sherry!
>=20
>=20
>> ---
>> ubuntu@imp1-vm:~/ltp-install$ sudo ./runltp -d /mnt -s chown02
>> INFO: ltp-pan reported all tests PASS
>> LTP Version: 20230127-112-gf41e8a2fa
>>=20
>> ubuntu@imp1-vm:~/ltp-install$ sudo ./runltp -d /mnt -s fchown02
>> INFO: ltp-pan reported all tests PASS
>> LTP Version: 20230127-112-gf41e8a2fa
>>=20
>> ubuntu@imp1-vm:~/src/git/xfstests$ sudo ./check -g perms
>> FSTYP         -- nfs
>> PLATFORM      -- Linux/x86_64 imp1-vm 6.3.0-nfs-setgid-3a3cfe624076 #20 =
SMP PREEMPT_DYNAMIC Tue May  2 12:35:51 UTC 2023
>> MKFS_OPTIONS  -- 127.0.0.1:/nfsscratch
>> MOUNT_OPTIONS -- -o vers=3D3,noacl 127.0.0.1:/nfsscratch /mnt/scratch
>> Passed all 41 tests
>> ---
>> fs/nfsd/vfs.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>=20
>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>> index bb9d47172162..c4ef24c5ffd0 100644
>> --- a/fs/nfsd/vfs.c
>> +++ b/fs/nfsd/vfs.c
>> @@ -388,7 +388,9 @@ nfsd_sanitize_attrs(struct inode *inode, struct iatt=
r *iap)
>> iap->ia_mode &=3D ~S_ISGID;
>> } else {
>> /* set ATTR_KILL_* bits and let VFS handle it */
>> - iap->ia_valid |=3D (ATTR_KILL_SUID | ATTR_KILL_SGID);
>> + iap->ia_valid |=3D ATTR_KILL_SUID;
>> + iap->ia_valid |=3D
>> + setattr_should_drop_sgid(&nop_mnt_idmap, inode);
>> }
>> }
>> }
>> --=20
>> 2.34.1
>>=20
>=20
> --
> Chuck Lever


--
Chuck Lever