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

Paul Moore
2023-07-07T21:44:20Z

On Fri, Jul 7, 2023 at 12:54 PM 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 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?
> >
> > 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.

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