[PATCH v6 05/11] LSM: Create lsm_module_list system call

[Casey Schaufler <casey@schaufler-ca.com>]

Create a system call to report the list of Linux Security Modules
that are active on the system. The list is provided as an array
of LSM ID numbers.

The calling application can use this list determine what LSM
specific actions it might take. That might include chosing an
output format, determining required privilege or bypassing
security module specific behavior.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 Documentation/userspace-api/lsm.rst |  3 ++
 include/linux/syscalls.h            |  1 +
 kernel/sys_ni.c                     |  1 +
 security/lsm_syscalls.c             | 43 ++++++++++++++++++++++++++++-
 4 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/Documentation/userspace-api/lsm.rst b/Documentation/userspace-api/lsm.rst
index b45e402302b3..ecdf1acd15b1 100644
--- a/Documentation/userspace-api/lsm.rst
+++ b/Documentation/userspace-api/lsm.rst
@@ -63,6 +63,9 @@ Get the specified security attributes of the current process
 .. kernel-doc:: security/lsm_syscalls.c
     :identifiers: sys_lsm_get_self_attr
 
+.. kernel-doc:: security/lsm_syscalls.c
+    :identifiers: sys_lsm_module_list
+
 Additional documentation
 ========================
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 1ef2a3de8ae0..9c947022a411 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1062,6 +1062,7 @@ asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long l
 asmlinkage long sys_lsm_get_self_attr(struct lsm_ctx *ctx, size_t *size,
 				      __u64 flags);
 asmlinkage long sys_lsm_set_self_attr(struct lsm_ctx *ctx, __u64 flags);
+asmlinkage long sys_lsm_module_list(u64 *ids, size_t *size, int flags);
 
 /*
  * Architecture-specific system calls
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d03c78ef1562..32784e271fa5 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -265,6 +265,7 @@ COND_SYSCALL(mremap);
 /* security/lsm_syscalls.c */
 COND_SYSCALL(lsm_get_self_attr);
 COND_SYSCALL(lsm_set_self_attr);
+COND_SYSCALL(lsm_module_list);
 
 /* security/keys/keyctl.c */
 COND_SYSCALL(add_key);
diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
index b89c4e7d009e..ccd3b236670b 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -19,7 +19,7 @@
 
 struct attrs_map {
 	char *name;
-	int attrs;
+	u64 attrs;
 };
 
 static const struct attrs_map lsm_attr_names[] = {
@@ -102,3 +102,44 @@ SYSCALL_DEFINE3(lsm_get_self_attr, struct lsm_ctx __user *, ctx,
 {
 	return security_getselfattr(flags, ctx, size);
 }
+
+/**
+ * sys_lsm_module_list - Return a list of the active security modules
+ * @ids: the LSM module ids
+ * @size: size of @ids, updated on return
+ * @flags: reserved for future use, must be zero
+ *
+ * Returns a list of the active LSM ids. On success this function
+ * returns the number of @ids array elements. This value may be zero
+ * if there are no LSMs active. If @size is insufficient to contain
+ * the return data -E2BIG is returned and @size is set to the minimum
+ * required size. In all other cases a negative value indicating the
+ * error is returned.
+ */
+SYSCALL_DEFINE3(lsm_module_list,
+		u64 __user *, ids,
+		size_t __user *, size,
+		u64, flags)
+{
+	size_t total_size = lsm_active_cnt * sizeof(*ids);
+	size_t usize;
+	int i;
+
+	if (flags)
+		return -EINVAL;
+
+	if (get_user(usize, size))
+		return -EFAULT;
+
+	if (put_user(total_size, size) != 0)
+		return -EFAULT;
+
+	if (usize < total_size)
+		return -E2BIG;
+
+	for (i = 0; i < lsm_active_cnt; i++)
+		if (put_user(lsm_idlist[i]->id, ids++))
+			return -EFAULT;
+
+	return lsm_active_cnt;
+}
-- 
2.39.0