[PATCH v1 7/8] LSM: Create lsm_module_list system call

[Casey Schaufler]

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 at schaufler-ca.com>
---
 include/linux/syscalls.h |  1 +
 kernel/sys_ni.c          |  1 +
 security/lsm_syscalls.c  | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 2d9033e9e5a0..02bb82142e24 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1058,6 +1058,7 @@ asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long l
 					    unsigned long home_node,
 					    unsigned long flags);
 asmlinkage long sys_lsm_self_attr(struct lsm_ctx *ctx, size_t *size, int flags);
+asmlinkage long sys_lsm_module_list(unsigned int *ids, size_t *size, int flags);
 
 /*
  * Architecture-specific system calls
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 0fdb0341251d..bde9e74a3473 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -264,6 +264,7 @@ COND_SYSCALL(mremap);
 
 /* security/lsm_syscalls.c */
 COND_SYSCALL(lsm_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 da0fab7065e2..cd5db370b974 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -154,3 +154,41 @@ SYSCALL_DEFINE3(lsm_self_attr,
 	kfree(final);
 	return rc;
 }
+
+/**
+ * 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,
+		unsigned int __user *, ids,
+		size_t __user *, size,
+		unsigned int, flags)
+{
+	size_t total_size = lsm_id * sizeof(*ids);
+	size_t usize;
+	int i;
+
+	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_id; i++)
+		if (put_user(lsm_idlist[i]->id, ids++))
+			return -EFAULT;
+
+	return lsm_id;
+}
-- 
2.37.3