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Subject: Re: [PATCH v12 1/4] security: Allow all LSMs to provide xattrs for
 inode_init_security hook
From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
To:     Paul Moore <paul@paul-moore.com>,
        Roberto Sassu <roberto.sassu@huawei.com>
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        "jmorris@namei.org" <jmorris@namei.org>,
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        "keescook@chromium.org" <keescook@chromium.org>,
        "nicolas.bouchinet@clip-os.org" <nicolas.bouchinet@clip-os.org>
Date:   Fri, 07 Jul 2023 16:42:39 +0200
In-Reply-To: <CAHC9VhQGWWQgA9DBpq+q4XQerbN0SXAB8RG94G8uMD0-J968xA@mail.gmail.com>
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         <1c8c612d99e202a61e6a6ecf50d4cace.paul@paul-moore.com>
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On Fri, 2023-07-07 at 10:34 -0400, Paul Moore wrote:
> On Fri, Jul 7, 2023 at 2:49 AM Roberto Sassu <roberto.sassu@huawei.com> wrote:
> > > From: Paul Moore [mailto:paul@paul-moore.com]
> > > Sent: Friday, July 7, 2023 3:44 AM
> > > 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 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@clip-os.org>
> > > > Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/
> > > > 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?
> > 
> > Hi Paul
> > 
> > yes, sure, I'm ok with them. Please make them during the merge.
> 
> Great, I'll queue this up for merging once the merge window closes.
> I'll send confirmation once it's done but just a heads-up that things
> might be a little delayed next week.

Ok, no problem.

Thanks!

Roberto