linux-kernel - Re: [PATCH v12 1/4] security: Allow all LSMs to provide xattrs for inode_init

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Date:   Tue, 11 Jul 2023 08:40:03 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Casey Schaufler <casey@...aufler-ca.com>, zohar@...ux.ibm.com,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        bpf@...r.kernel.org, kpsingh@...nel.org, keescook@...omium.org,
        nicolas.bouchinet@...p-os.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v12 1/4] security: Allow all LSMs to provide xattrs for
 inode_init_security hook

On Mon, 2023-07-10 at 14:04 -0400, Paul Moore wrote:
> On Fri, Jul 7, 2023 at 5:44 PM Paul Moore <paul@...l-moore.com> wrote:
> > On Fri, Jul 7, 2023 at 12:54 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> > > On 7/6/2023 6:43 PM, Paul Moore wrote:
> > > > On Jun 10, 2023 Roberto Sassu <roberto.sassu@...weicloud.com> wrote:
> > > > > Currently, the LSM infrastructure supports only one LSM providing an xattr
> > > > > and EVM calculating the HMAC on that xattr, plus other inode metadata.
> > > > > 
> > > > > Allow all LSMs to provide one or multiple xattrs, by extending the security
> > > > > blob reservation mechanism. Introduce the new lbs_xattr_count field of the
> > > > > lsm_blob_sizes structure, so that each LSM can specify how many xattrs it
> > > > > needs, and the LSM infrastructure knows how many xattr slots it should
> > > > > allocate.
> > > > > 
> > > > > Modify the inode_init_security hook definition, by passing the full
> > > > > xattr array allocated in security_inode_init_security(), and the current
> > > > > number of xattr slots in that array filled by LSMs. The first parameter
> > > > > 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 number of
> > > > > filled xattrs, so that at the next invocation it returns the next xattr
> > > > > 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@...p-os.org>
> > > > > Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/
> > > > > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.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.

Thanks Paul, also for making the patch set better!

Roberto