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SubjectRe: [PATCH net-next v7 05/10] landlock: Add LSM hooks related to filesystem
On Mon, Aug 21, 2017 at 02:09:28AM +0200, Mickaël Salaün wrote:
> Handle 33 filesystem-related LSM hooks for the Landlock filesystem
> event: LANDLOCK_SUBTYPE_EVENT_FS.
>
> A Landlock event wrap LSM hooks for similar kernel object types (e.g.
> struct file, struct path...). Multiple LSM hooks can trigger the same
> Landlock event.
>
> Landlock handle nine coarse-grained actions: read, write, execute, new,
> get, remove, ioctl, lock and fcntl. Each of them abstract LSM hook
> access control in a way that can be extended in the future.
>
> The Landlock LSM hook registration is done after other LSM to only run
> actions from user-space, via eBPF programs, if the access was granted by
> major (privileged) LSMs.
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

...

> +/* WRAP_ARG_SB */
> +#define WRAP_ARG_SB_TYPE WRAP_TYPE_FS
> +#define WRAP_ARG_SB_DEC(arg) \
> + EXPAND_C(WRAP_TYPE_FS) wrap_##arg = \
> + { .type = BPF_HANDLE_FS_TYPE_DENTRY, .dentry = arg->s_root };
> +#define WRAP_ARG_SB_VAL(arg) ((uintptr_t)&wrap_##arg)
> +#define WRAP_ARG_SB_OK(arg) (arg && arg->s_root)
...

> +HOOK_NEW_FS(sb_remount, 2,
> + struct super_block *, sb,
> + void *, data,
> + WRAP_ARG_SB, sb,
> + WRAP_ARG_RAW, LANDLOCK_ACTION_FS_WRITE
> +);

this looks wrong. casting super_block to dentry?

> +/* a directory inode contains only one dentry */
> +HOOK_NEW_FS(inode_create, 3,
> + struct inode *, dir,
> + struct dentry *, dentry,
> + umode_t, mode,
> + WRAP_ARG_INODE, dir,
> + WRAP_ARG_RAW, LANDLOCK_ACTION_FS_WRITE
> +);

more general question: why you're not wrapping all useful
arguments? Like in the above dentry can be acted upon
by the landlock rule and it's readily available...

The limitation of only 2 args looks odd.
Is it a hard limitation ? how hard to extend?

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