On 22/02/2023 21:08, Casey Schaufler wrote:
Create a system call lsm_get_self_attr() to provide the security
module maintained attributes of the current process.
Create a system call lsm_set_self_attr() to set a security
module maintained attribute of the current process.
Historically these attributes have been exposed to user space via
entries in procfs under /proc/self/attr.
The attribute value is provided in a lsm_ctx structure. The structure
identifys the size of the attribute, and the attribute value. The format
of the attribute value is defined by the security module. A flags field
is included for LSM specific information. It is currently unused and must
be 0. The total size of the data, including the lsm_ctx structure and any
padding, is maintained as well.
struct lsm_ctx {
__u64 id;
__u64 flags;
__u64 len;
__u64 ctx_len;
__u8 ctx[];
};
Two new LSM hooks are used to interface with the LSMs.
security_getselfattr() collects the lsm_ctx values from the
LSMs that support the hook, accounting for space requirements.
security_setselfattr() identifies which LSM the attribute is
intended for and passes it along.
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
Documentation/userspace-api/lsm.rst | 15 ++++
include/linux/lsm_hook_defs.h | 4 ++
include/linux/lsm_hooks.h | 9 +++
include/linux/security.h | 19 +++++
include/linux/syscalls.h | 4 ++
include/uapi/linux/lsm.h | 33 +++++++++
kernel/sys_ni.c | 4 ++
security/Makefile | 1 +
security/lsm_syscalls.c | 104 ++++++++++++++++++++++++++++
security/security.c | 82 ++++++++++++++++++++++
10 files changed, 275 insertions(+)
create mode 100644 security/lsm_syscalls.c
[...]
+/**
+ * security_setselfattr - Set an LSM attribute on the current process.
+ * @attr: which attribute to return
+ * @ctx: the user-space source for the information
+ * @size: the size of the data
+ *
+ * Set an LSM attribute for the current process. The LSM, attribute
+ * and new value are included in @ctx.
+ *
+ * Returns 0 on seccess, an LSM specific value on failure.
+ */
+int security_setselfattr(u64 __user attr, struct lsm_ctx __user *ctx,
+ size_t __user size)
+{
+ struct security_hook_list *hp;
+ struct lsm_ctx lctx;
+
+ if (size < sizeof(*ctx))
If the lsm_ctx struct could grow in the future, we should check the size
of the struct to the last field for compatibility reasons, see
Landlock's copy_min_struct_from_user().
+ return -EINVAL;
+ if (copy_from_user(&lctx, ctx, sizeof(*ctx)))
+ return -EFAULT;
+
+ hlist_for_each_entry(hp, &security_hook_heads.setselfattr, list)
+ if ((hp->lsmid->id) == lctx.id)
+ return hp->hook.setselfattr(attr, ctx, size);
+
+ return LSM_RET_DEFAULT(setselfattr);
+}
+
int security_getprocattr(struct task_struct *p, int lsmid, const char *name,
char **value)
{
