On 19/04/2017 00:17, Kees Cook wrote: > On Tue, Mar 28, 2017 at 4:46 PM, 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. >> >> 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 >> Cc: Alexei Starovoitov >> Cc: Andy Lutomirski >> Cc: Daniel Borkmann >> Cc: David S. Miller >> Cc: James Morris >> Cc: Kees Cook >> Cc: Serge E. Hallyn >> --- >> 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. This is useful to catch defined but unused hooks: error out if a HOOK_NEW_FS(foo) is not used with a HOOK_INIT_FS(foo) in the struct security_hook_list landlock_hooks. > >> [...] >> @@ -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")? Yes, this is ugly with the new security_add_hooks() with three arguments but I wanted to split the hooks definition in multiple files. The current security_add_hooks() use lsm_append(lsm, &lsm_names) which is not exported. Unfortunately, calling multiple security_add_hooks() with the same LSM name would register multiple names for the same LSM… Is it OK if I modify this function to not add duplicated entries? > >> +} >> 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? Right, this is the intend. I'm not sure it is the only way to register hooks, though. For an unprivileged access-control, we don't want to give the ability to any process to do some checks, through an eBPF program, on kernel objects (e.g. files) if they should not be accessible (because of a following LSM hook check). Mickaël