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SubjectRe: [PATCH net-next v6 04/11] landlock: Add LSM hooks related to filesystem
On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <mic@digikod.net> 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.
>
> Changes since v5:
> * split hooks.[ch] into hooks.[ch] and hooks_fs.[ch]
> * add more documentation
> * cosmetic fixes
>
> Changes since v4:
> * add LSM hook abstraction called Landlock event
> * use the compiler type checking to verify hooks use by an event
> * handle all filesystem related LSM hooks (e.g. file_permission,
> mmap_file, sb_mount...)
> * register BPF programs for Landlock just after LSM hooks registration
> * move hooks registration after other LSMs
> * add failsafes to check if a hook is not used by the kernel
> * allow partial raw value access form the context (needed for programs
> generated by LLVM)
>
> Changes since v3:
> * split commit
> * add hooks dealing with struct inode and struct path pointers:
> inode_permission and inode_getattr
> * add abstraction over eBPF helper arguments thanks to wrapping structs
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: James Morris <james.l.morris@oracle.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Serge E. Hallyn <serge@hallyn.com>
> ---
> include/linux/lsm_hooks.h | 5 +
> security/landlock/Makefile | 4 +-
> security/landlock/hooks.c | 115 +++++++++
> security/landlock/hooks.h | 177 ++++++++++++++
> security/landlock/hooks_fs.c | 563 +++++++++++++++++++++++++++++++++++++++++++
> security/landlock/hooks_fs.h | 19 ++
> security/landlock/init.c | 13 +
> security/security.c | 7 +-
> 8 files changed, 901 insertions(+), 2 deletions(-)
> create mode 100644 security/landlock/hooks.c
> create mode 100644 security/landlock/hooks.h
> create mode 100644 security/landlock/hooks_fs.c
> create mode 100644 security/landlock/hooks_fs.h
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index e29d4c62a3c8..884289166a0e 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1920,5 +1920,10 @@ void __init loadpin_add_hooks(void);
> #else
> static inline void loadpin_add_hooks(void) { };
> #endif
> +#ifdef CONFIG_SECURITY_LANDLOCK
> +extern void __init landlock_add_hooks(void);
> +#else
> +static inline void __init landlock_add_hooks(void) { }
> +#endif /* CONFIG_SECURITY_LANDLOCK */
>
> #endif /* ! __LINUX_LSM_HOOKS_H */
> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
> index 7205f9a7a2ee..c0db504a6335 100644
> --- a/security/landlock/Makefile
> +++ b/security/landlock/Makefile
> @@ -1,3 +1,5 @@
> +ccflags-$(CONFIG_SECURITY_LANDLOCK) += -Werror=unused-function

Why is this needed? If it can't be avoided, a comment should exist
here explaining why.

> [...]
> @@ -127,3 +132,11 @@ static struct bpf_prog_type_list bpf_landlock_type __ro_after_init = {
> .ops = &bpf_landlock_ops,
> .type = BPF_PROG_TYPE_LANDLOCK,
> };
> +
> +void __init landlock_add_hooks(void)
> +{
> + pr_info("landlock: Version %u", LANDLOCK_VERSION);
> + landlock_add_hooks_fs();
> + security_add_hooks(NULL, 0, "landlock");
> + bpf_register_prog_type(&bpf_landlock_type);

I'm confused by the separation of hook registration here. The call to
security_add_hooks is with count=0 is especially weird. Why isn't this
just a single call with security_add_hooks(landlock_hooks,
ARRAY_SIZE(landlock_hooks), "landlock")?

> +}
> diff --git a/security/security.c b/security/security.c
> index d0e07f269b2d..a3e9f4625991 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -64,10 +64,15 @@ int __init security_init(void)
> loadpin_add_hooks();
>
> /*
> - * Load all the remaining security modules.
> + * Load all remaining privileged security modules.
> */
> do_security_initcalls();
>
> + /*
> + * Load potentially-unprivileged security modules at the end.
> + */
> + landlock_add_hooks();

Oh, is this to make it last in the list? Is there a reason it has to be last?

-Kees

--
Kees Cook
Pixel Security

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