Date: Thu, 27 Feb 2020 23:11:48 +0100 From: Peter Eriksson <pen@lysator.liu.se> To: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Linux could write to read only files on FreeBSD NFS server Message-ID: <6EC06026-DA28-4CAC-8D56-5C7856D4625E@lysator.liu.se> In-Reply-To: <707243CD-C67E-4DAD-AC5A-68EC11CFFDFD@lysator.liu.se> References: <CAHJqQjuEVpL4xV1dAf6scFqFfMNm1gY3jOaO64ZQJTCQi_qzcQ@mail.gmail.com> <707243CD-C67E-4DAD-AC5A-68EC11CFFDFD@lysator.liu.se>
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I see that this was a bit unclear, writing to the protected file was via =
NFS from a Linux (CentOS 7) client. I verified the ACLs and the file =
content both via NFSv4 and locally on the FreeBSD server.
Writing from an OmniOS (OpenSolaris) client fails. As does a local =
write. As it should...
Also, it=E2=80=99s not related to ACLs (atleast not directly). Using =
=E2=80=9Cchmod=E2=80=9D gives the same effect:
> $ rm -f x
> $ touch x
> $ chmod 000 x
> $ ls -l x
> ---------- 1 peter86 employee-liu.se 0 27 feb 22.46 x
> $ echo foo >x
> $ cat x
> cat: x: Permission denied
> $ chmod 600 x
> cat x
> foo
Rick:
Looking at a tcpdump capture of the NFS traffic from the Linux client it =
seems to be doing:
1. Client -> Server:
V4 Procedure: COMPOUND (1)
SEQUENCE (53)
PUTFH (22)
OPEN (18)=20
share_access: OPEN4_SHARE_ACCESS_WRITE
open type: OPEN4_NOCREATE
ACCESS (3)
Check: RD MD XT XE
GETATTR (9)
2. Server -> Client:
V4 Procedure: COMPOUND (1)
Status: NFS4_OK
Operations (5):
SEQUENCE (53)
Status: NFS4_OK
PUTFH
Status: NFS4_OK
OPEN
Status: NFS4_OK
ACCESS [Access Denied]
Status: NFS4_OK
GETATTR
Status: NFS4_OK
3. Client -> Server:
V4 Procedure: COMPOUND (1)
Tag: <EMPTY>
Operations:
SEQUENCE (53)=20
PUTFH (22)
WRITE (38)
Stable: FILE_SYNC4
GETATTR (9)
4. Server -> Client
V4 Procedure: COMPOUND
Tag: <EMPTY>
Operations:
SEQUENCE (53)
Status: NFS4_OK
PUTFH
Status: NFS4_OK
WRITE
Status: NFS4_OK
Committed: FILE_SYNC4
GETATTR
Status: NFS4_OK
(According to Wireshark)
Looks like Linux ignores the Access Denied in packet 2 and just forges =
ahead, and FreeBSD happily accepts the WRITE in packet 3=E2=80=A6
- Peter
> On 27 Feb 2020, at 22:03, Peter Eriksson <pen@lysator.liu.se> wrote:
>=20
> I can verify that this indeed seems to be the case - the file owner =
can always write to files, no matter the permissions set.
>=20
> Tested both locally (on ZFS) and over NFS (from the same directory).
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