Re: [PATCH v12 1/4] security: Allow all LSMs to provide xattrs for inode_init_security hook

[Paul Moore]

On Fri, Jul 7, 2023 at 5:44 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> On Fri, Jul 7, 2023 at 12:54 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
> > On 7/6/2023 6:43 PM, Paul Moore wrote:
> > > On Jun 10, 2023 Roberto Sassu <roberto.sassu@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxx>
> > >> Link: https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/
> > >> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > >> ---
> > >>  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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