[PATCH v4 3/5] security: Allow all LSMs to provide xattrs for inode_init_security hook

[Roberto Sassu]

On 11/17/2022 6:18 PM, Casey Schaufler wrote:
> On 11/17/2022 8:05 AM, Mimi Zohar wrote:
>> hOn Thu, 2022-11-10 at 10:46 +0100, Roberto Sassu wrote:
>>> From: Roberto Sassu <roberto.sassu at huawei.com>
>>>
>>> Currently, security_inode_init_security() 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 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.
>> Perhaps supporting per LSM multiple xattrs is a nice idea, but EVM
>> doesn't currently support it.  The LSM xattrs are hard coded in
>> evm_config_default_xattrnames[],  based on whether the LSM is
>> configured.  Additional security xattrs may be included in the
>> security.evm calculation, by extending the list via
>> security/integrity/evm/evm_xattrs.
> 
> Smack uses multiple xattrs. All file system objects have a SMACK64
> attribute, which is used for access control. A program file may have
> a SMACK64EXEC attribute, which is the label the program will run with.
> A library may have a SMACK64MMAP attribute to restrict loading. A
> directory may have a SMACK64TRANSMUTE attribute, which modifies the
> new object creation behavior.
> 
> The point being that it may be more than a "nice idea" to support
> multiple xattrs. It's not a hypothetical situation.

Ok, that means that I have to change the number of xattrs reserved by 
Smack in patch 3.

Thanks

Roberto