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From:   Paul Moore <paul@paul-moore.com>
Date:   Mon, 10 Jul 2023 14:04:58 -0400
Message-ID: <CAHC9VhSFy6wf+7DXrG=6CXZC4RrpTeP2sQezX0BPc95fxGAWxQ@mail.gmail.com>
Subject: Re: [PATCH v12 1/4] security: Allow all LSMs to provide xattrs for
 inode_init_security hook
To:     Roberto Sassu <roberto.sassu@huaweicloud.com>
Cc:     Casey Schaufler <casey@schaufler-ca.com>, zohar@linux.ibm.com,
        dmitry.kasatkin@gmail.com, jmorris@namei.org, serge@hallyn.com,
        stephen.smalley.work@gmail.com, eparis@parisplace.org,
        linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
        bpf@vger.kernel.org, kpsingh@kernel.org, keescook@chromium.org,
        nicolas.bouchinet@clip-os.org,
        Roberto Sassu <roberto.sassu@huawei.com>
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On Fri, Jul 7, 2023 at 5:44=E2=80=AFPM Paul Moore <paul@paul-moore.com> wro=
te:
> On Fri, Jul 7, 2023 at 12:54=E2=80=AFPM Casey Schaufler <casey@schaufler-=
ca.com> wrote:
> > On 7/6/2023 6:43 PM, Paul Moore wrote:
> > > On Jun 10, 2023 Roberto Sassu <roberto.sassu@huaweicloud.com> wrote:
> > >> Currently, the LSM infrastructure supports only one LSM providing an=
 xattr
> > >> and EVM calculating the HMAC on that xattr, plus other inode metadat=
a.
> > >>
> > >> Allow all LSMs to provide one or multiple xattrs, by extending the s=
ecurity
> > >> blob reservation mechanism. Introduce the new lbs_xattr_count field =
of the
> > >> lsm_blob_sizes structure, so that each LSM can specify how many xatt=
rs it
> > >> needs, and the LSM infrastructure knows how many xattr slots it shou=
ld
> > >> allocate.
> > >>
> > >> Modify the inode_init_security hook definition, by passing the full
> > >> xattr array allocated in security_inode_init_security(), and the cur=
rent
> > >> number of xattr slots in that array filled by LSMs. The first parame=
ter
> > >> would allow EVM to access and calculate the HMAC on xattrs supplied =
by
> > >> other LSMs, the second to not leave gaps in the xattr array, when an=
 LSM
> > >> requested but did not provide xattrs (e.g. if it is not initialized)=
.
> > >>
> > >> Introduce lsm_get_xattr_slot(), which LSMs can call as many times as=
 the
> > >> number specified in the lbs_xattr_count field of the lsm_blob_sizes
> > >> structure. During each call, lsm_get_xattr_slot() increments the num=
ber of
> > >> filled xattrs, so that at the next invocation it returns the next xa=
ttr
> > >> slot to fill.
> > >>
> > >> Cleanup security_inode_init_security(). Unify the !initxattrs and
> > >> initxattrs case by simply not allocating the new_xattrs array in the
> > >> former. Update the documentation to reflect the changes, and fix the
> > >> description of the xattr name, as it is not allocated anymore.
> > >>
> > >> Adapt both SELinux and Smack to use the new definition of the
> > >> inode_init_security hook, and to call lsm_get_xattr_slot() to obtain=
 and
> > >> fill the reserved slots in the xattr array.
> > >>
> > >> Move the xattr->name assignment after the xattr->value one, so that =
it is
> > >> done only in case of successful memory allocation.
> > >>
> > >> Finally, change the default return value of the inode_init_security =
hook
> > >> from zero to -EOPNOTSUPP, so that BPF LSM correctly follows the hook
> > >> conventions.
> > >>
> > >> Reported-by: Nicolas Bouchinet <nicolas.bouchinet@clip-os.org>
> > >> Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archl=
inux/
> > >> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> > >> ---
> > >>  include/linux/lsm_hook_defs.h |  6 +--
> > >>  include/linux/lsm_hooks.h     | 20 ++++++++++
> > >>  security/security.c           | 71 +++++++++++++++++++++++---------=
---
> > >>  security/selinux/hooks.c      | 17 +++++----
> > >>  security/smack/smack_lsm.c    | 25 ++++++------
> > >>  5 files changed, 92 insertions(+), 47 deletions(-)
> > > Two *very* small suggestions below, but I can make those during the
> > > merge if you are okay with that Roberto?
> > >
> > > I'm also going to assume that Casey is okay with the Smack portion of
> > > this patchset?  It looks fine to me, and considering his ACK on the
> > > other Smack patch in this patchset I'm assuming he is okay with this
> > > one as well ... ?
> >
> > Yes, please feel free to add my Acked-by as needed.
>
> Done.  Thanks Casey.

I'm merging the full patchset into lsm/next right now.  Thanks for all
your work on this Roberto, and a thank you for everyone else who
helped with reviews, testing, etc.

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