On 19/04/2017 00:17, Kees Cook wrote: > On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <[email protected]> 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 <[email protected]> >> Cc: Alexei Starovoitov <[email protected]> >> Cc: Andy Lutomirski <[email protected]> >> Cc: Daniel Borkmann <[email protected]> >> Cc: David S. Miller <[email protected]> >> Cc: James Morris <[email protected]> >> Cc: Kees Cook <[email protected]> >> Cc: Serge E. Hallyn <[email protected]> >> --- >> 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
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