New skb extension for use by LSMs (skb "security blob")?

[Casey Schaufler]

On 8/22/2019 1:15 PM, Florian Westphal wrote:
> Casey Schaufler <casey at schaufler-ca.com> wrote:
>> Given that the original objection to using a skb extension for a
>> security blob was that an extension is dynamic, and that the ubiquitous
>> nature of LSM use makes that unreasonable, it would seem that supporting
>> the security blob as a basic part if the skb would be the obvious and
>> correct solution. If the normal case is that there is an LSM that would
>> befit from the native (unextended) support of a blob, it would seem
>> that that is the case that should be optimized.
> What is this "blob"? i.e., what would you like to add to sk_buff to make
> whatever use cases you have in mind work?

In LSM terminology a blob is a set of data managed and used by
the LSM (either in the infrastructure or the security module).
Blob pointers are included in the system data structures to which
they relate. The inode has an i_security field, which is a void *.
If the secmark where replaced by a security blob, the u32 secmark field
in an sk_buff would be replaced by a void * security field.