[Virtio-fs] [PATCH v3 3/6] fuse: setattr should set FATTR_KILL_PRIV upon size change

[Harry G. Coin]

I suggest default settings meet this test:  A Fedora vm booted directly
via virtio FS (with virtiofs as root) running with SE enabled, with
xattr 'on' and the host fs xattr capable like btrfs (Fedora default) --
does not generate SE linux denials or 'attribute not settable'
complaints.  In other words -- 'it just works'.  At least in the default
fedora at this time that is not the case.

HC



On 11/11/20 7:54 AM, Miklos Szeredi wrote:
> On Fri, Nov 6, 2020 at 6:18 PM Vivek Goyal <vgoyal at redhat.com> wrote:
>
>> I think it does not hurt to start passing FATTR_KILL_PRIV for chown()
>> as well. In that case, server will always clear caps on chown but
>> clear suid/sgid only if FATTR_KILL_PRIV is set. (Which will always
>> be set).
> Okay.
>
> More thoughts for FUSE_HANDLE_KILLPRIV_V2:
>
>  - clear "security.capability" on write, truncate and chown unconditionally
>  - clear suid/sgid if
>     o setattr has FATTR_SIZE and  FATTR_KILL_PRIV
>     o setattr has FATTR_UID or FATTR_GID
>     o open has O_TRUNC and FUSE_OPEN_KILL_PRIV
>     o write has FUSE_WRITE_KILL_PRIV
>
> Kernel has:
> ATTR_KILL_PRIV -> clear "security.capability"
> ATTR_KILL_SUID -> clear S_ISUID
> ATTR_KILL_SGID -> clear S_ISGID if executable
>
> Fuse has:
> FUSE_*KILL_PRIV -> clear S_ISUID and S_ISGID if executable
>
> So the fuse meaning of FUSE_*KILL_PRIV has a complementary meaning to
> that of ATTR_KILL_PRIV, which is somewhat confusing.  Also "PRIV"
> implies all privileges, including "security.capability" but the fuse
> ones relate to suid/sgid only.
>
> How about FUSE_*KILL_SUIDGID (FUSE_WRITE_KILL_SUIDGID being an alias
> for FUSE_WRITE_KILL_PRIV)?
>
> Thanks,
> Miklos
>
>
>
>
>> So anything is fine. We just need to document it well. I think I will
>> write it very clearly in qemu patch depending on what goes in kernel.
>>
>> Thanks
>> Vivek
>>
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