[PATCH v10 05/11] LSM: Create lsm_list_modules 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 choosing an
output format, determining required privilege or bypassing
security module specific behavior.

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Kees Cook <keescook at chromium.org>
---
 Documentation/userspace-api/lsm.rst |  3 +++
 include/linux/syscalls.h            |  1 +
 kernel/sys_ni.c                     |  1 +
 security/lsm_syscalls.c             | 39 +++++++++++++++++++++++++++++
 4 files changed, 44 insertions(+)

diff --git a/Documentation/userspace-api/lsm.rst b/Documentation/userspace-api/lsm.rst
index e6c3f262addc..9edae18a2688 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_list_modules
+
 Additional documentation
 ========================
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 9a94c31bf6b6..ddbcc333f3c3 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1063,6 +1063,7 @@ asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx *ctx,
 				      size_t *size, __u32 flags);
 asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx *ctx,
 				      size_t size, __u32 flags);
+asmlinkage long sys_lsm_list_modules(u64 *ids, size_t *size, u32 flags);
 
 /*
  * Architecture-specific system calls
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d03c78ef1562..ceb3d21a62d0 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_list_modules);
 
 /* security/keys/keyctl.c */
 COND_SYSCALL(add_key);
diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
index ee3881159241..b89cccb2f123 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -53,3 +53,42 @@ SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr, struct lsm_ctx __user *,
 {
 	return security_getselfattr(attr, ctx, size, flags);
 }
+
+/**
+ * sys_lsm_list_modules - 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_list_modules, u64 __user *, ids, size_t __user *, size,
+		u32, 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;
+}
-- 
2.39.2