Re: [RFC v3 21/22] bpf,landlock: Add optional skb pointer in the Landlock context

On 14/09/2016 23:20, Alexei Starovoitov wrote:

On Wed, Sep 14, 2016 at 09:24:14AM +0200, Mickaël Salaün wrote:

quoted

This is a proof of concept to expose optional values that could depend
of the process access rights.

There is two dedicated flags: LANDLOCK_FLAG_ACCESS_SKB_READ and
LANDLOCK_FLAG_ACCESS_SKB_WRITE. Each of them can be activated to access
eBPF functions manipulating a skb in a read or write way.

Signed-off-by: Mickaël Salaün <mic@digikod.net>

...

quoted

 /* Handle check flags */
 #define LANDLOCK_FLAG_FS_DENTRY		(1 << 0)

@@ -619,12 +621,15 @@ struct landlock_handle {
  * @args: LSM hook arguments, see include/linux/lsm_hooks.h for there
  *        description and the LANDLOCK_HOOK* definitions from
  *        security/landlock/lsm.c for their types.
+ * @opt_skb: optional skb pointer, accessible with the
+ *           LANDLOCK_FLAG_ACCESS_SKB_* flags for network-related hooks.
  */
 struct landlock_data {
 	__u32 hook; /* enum landlock_hook_id */
 	__u16 origin; /* LANDLOCK_FLAG_ORIGIN_* */
 	__u16 cookie; /* seccomp RET_LANDLOCK */
 	__u64 args[6];
+	__u64 opt_skb;
 };

missing something here.
This patch doesn't make use of it.
That's something for the future?
How that field will be populated?
Why make it different vs the rest or args[6] ?

I don't use this code, it's only purpose is to show how to deal with
fine-grained privileges of Landlock programs (to allow Sargun to add his
custom helpers from Checmate). However, this optional field may be part
of args[6].