[PATCH v38 39/39] 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.

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
---
 arch/x86/entry/syscalls/syscall_64.tbl |  1 +
 include/linux/syscalls.h               |  1 +
 include/uapi/asm-generic/unistd.h      |  5 ++-
 kernel/sys_ni.c                        |  1 +
 security/lsm_syscalls.c                | 50 ++++++++++++++++++++++++++
 5 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 56d5c5202fd0..40b35e7069a7 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -373,6 +373,7 @@
 449	common	futex_waitv		sys_futex_waitv
 450	common	set_mempolicy_home_node	sys_set_mempolicy_home_node
 451	common	lsm_self_attr		sys_lsm_self_attr
+452	common	lsm_module_list		sys_lsm_module_list
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 7f87ef8be546..e2e2a9e93e8c 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1057,6 +1057,7 @@ 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/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index aa66718e1b48..090617a9a53a 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -889,8 +889,11 @@ __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
 #define __NR_lsm_self_attr 451
 __SYSCALL(__NR_lsm_self_attr, sys_lsm_self_attr)
 
+#define __NR_lsm_module_list 452
+__SYSCALL(__NR_lsm_module_list, sys_lsm_module_list)
+
 #undef __NR_syscalls
-#define __NR_syscalls 452
+#define __NR_syscalls 453
 
 /*
  * 32 bit systems traditionally used different
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..41d9ef945ede 100644
--- a/security/lsm_syscalls.c
+++ b/security/lsm_syscalls.c
@@ -154,3 +154,53 @@ 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,
+	       int, flags)
+{
+	unsigned int *interum;
+	size_t total_size = lsm_id * sizeof(*interum);
+	size_t usize;
+	int rc;
+	int i;
+
+	if (get_user(usize, size))
+		return -EFAULT;
+
+	if (usize < total_size) {
+		if (put_user(total_size, size) != 0)
+			return -EFAULT;
+		return -E2BIG;
+	}
+
+	interum = kzalloc(total_size, GFP_KERNEL);
+	if (interum == NULL)
+		return -ENOMEM;
+
+	for (i = 0; i < lsm_id; i++)
+		interum[i] = lsm_idlist[i]->id;
+
+	if (copy_to_user(ids, interum, total_size) != 0 ||
+	    put_user(total_size, size) != 0)
+		rc = -EFAULT;
+	else
+		rc = lsm_id;
+
+	kfree(interum);
+	return rc;
+}
-- 
2.37.3