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

[Mimi Zohar <zohar@linux.ibm.com>]

On Thu, 2022-11-17 at 09:18 -0800, 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@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.

And each of these addiitonal Smack xattrs are already defined in 
evm_config_default_xattrnames[].

Mimi