On 6/7/2024 5:53 AM, Paul Moore wrote:
On Thu, Apr 11, 2024 at 8:24 AM Xu Kuohai xukuohai@huaweicloud.com wrote:
From: Xu Kuohai xukuohai@huawei.com
Add macro LSM_RET_INT to annotate lsm hook return integer type and the default return value, and the expected return range.
The LSM_RET_INT is declared as:
LSM_RET_INT(defval, min, max)
where
defval is the default return value
min and max indicate the expected return range is [min, max]
The return value range for each lsm hook is taken from the description in security/security.c.
The expanded result of LSM_RET_INT is not changed, and the compiled product is not changed.
Signed-off-by: Xu Kuohai xukuohai@huawei.com
include/linux/lsm_hook_defs.h | 591 +++++++++++++++++----------------- include/linux/lsm_hooks.h | 6 - kernel/bpf/bpf_lsm.c | 10 + security/security.c | 1 + 4 files changed, 313 insertions(+), 295 deletions(-)
...
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 334e00efbde4..708f515ffbf3 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -18,435 +18,448 @@
- The macro LSM_HOOK is used to define the data structures required by
- the LSM framework using the pattern:
LSM_HOOK(<return_type>, <default_value>, <hook_name>, args...)
LSM_HOOK(<return_type>, <return_description>, <hook_name>, args...)- struct security_hook_heads {
- #define LSM_HOOK(RET, DEFAULT, NAME, ...) struct hlist_head NAME;
*/
- #define LSM_HOOK(RET, RETVAL_DESC, NAME, ...) struct hlist_head NAME;
- #include <linux/lsm_hook_defs.h>
- #undef LSM_HOOK
- };
-LSM_HOOK(int, 0, binder_set_context_mgr, const struct cred *mgr) -LSM_HOOK(int, 0, binder_transaction, const struct cred *from, +LSM_HOOK(int, LSM_RET_INT(0, -MAX_ERRNO, 0), binder_set_context_mgr, const struct cred *mgr) +LSM_HOOK(int, LSM_RET_INT(0, -MAX_ERRNO, 0), binder_transaction, const struct cred *from, const struct cred *to) -LSM_HOOK(int, 0, binder_transfer_binder, const struct cred *from, +LSM_HOOK(int, LSM_RET_INT(0, -MAX_ERRNO, 0), binder_transfer_binder, const struct cred *from, const struct cred *to) -LSM_HOOK(int, 0, binder_transfer_file, const struct cred *from, +LSM_HOOK(int, LSM_RET_INT(0, -MAX_ERRNO, 0), binder_transfer_file, const struct cred *from, const struct cred *to, const struct file *file)
I'm not overly excited about injecting these additional return value range annotations into the LSM hook definitions, especially since the vast majority of the hooks "returns 0 on success, negative values on error". I'd rather see some effort put into looking at the feasibility of converting some (all?) of the LSM hook return value exceptions into the more conventional 0/-ERRNO format. Unfortunately, I haven't had the time to look into that myself, but if you wanted to do that I think it would be a good thing.
I agree that keeping all hooks return a consistent range of 0/-ERRNO is more elegant than adding return value range annotations. However, there are two issues that might need to be addressed first:
1. Compatibility
For instance, security_vm_enough_memory_mm() determines whether to set cap_sys_admin by checking if the hook vm_enough_memory returns a positive number. If we were to change the hook vm_enough_memory to return 0 to indicate the need for cap_sys_admin, then for the LSM BPF program currently returning 0, the interpretation of its return value would be reversed after the modification.
2. Expressing multiple non-error states using 0/-ERRNO
IIUC, although 0/-ERRNO can be used to express different errors, only 0 can be used for non-error state. If there are multiple non-error states, they cannot be distinguished. For example, security_inode_need_killpriv() returns < 0 on error, 0 if security_inode_killpriv() doesn't need to be called, and > 0 if security_inode_killpriv() does need to be called.