seccomp: Separate read and write code for actions_logged sysctl

Break the read and write paths of the kernel.seccomp.actions_logged
sysctl into separate functions to maintain readability. An upcoming
change will need to audit writes, but not reads, of this sysctl which
would introduce too many conditional code paths on whether or not the
'write' parameter evaluates to true.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/seccomp.c

@@ -1199,48 +1199,64 @@ static bool seccomp_actions_logged_from_names(u32 *actions_logged, char *names)
 	return true;
 }
 
-static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write,
-					  void __user *buffer, size_t *lenp,
-					  loff_t *ppos)
+static int read_actions_logged(struct ctl_table *ro_table, void __user *buffer,
+			       size_t *lenp, loff_t *ppos)
 {
 	char names[sizeof(seccomp_actions_avail)];
 	struct ctl_table table;
+
+	memset(names, 0, sizeof(names));
+
+	if (!seccomp_names_from_actions_logged(names, sizeof(names),
+					       seccomp_actions_logged))
+		return -EINVAL;
+
+	table = *ro_table;
+	table.data = names;
+	table.maxlen = sizeof(names);
+	return proc_dostring(&table, 0, buffer, lenp, ppos);
+}
+
+static int write_actions_logged(struct ctl_table *ro_table, void __user *buffer,
+				size_t *lenp, loff_t *ppos)
+{
+	char names[sizeof(seccomp_actions_avail)];
+	struct ctl_table table;
+	u32 actions_logged;
 	int ret;
 
-	if (write && !capable(CAP_SYS_ADMIN))
+	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	memset(names, 0, sizeof(names));
 
-	if (!write) {
-		if (!seccomp_names_from_actions_logged(names, sizeof(names),
-						       seccomp_actions_logged))
-			return -EINVAL;
-	}
-
 	table = *ro_table;
 	table.data = names;
 	table.maxlen = sizeof(names);
-	ret = proc_dostring(&table, write, buffer, lenp, ppos);
+	ret = proc_dostring(&table, 1, buffer, lenp, ppos);
 	if (ret)
 		return ret;
 
-	if (write) {
-		u32 actions_logged;
-
-		if (!seccomp_actions_logged_from_names(&actions_logged,
-						       table.data))
-			return -EINVAL;
-
-		if (actions_logged & SECCOMP_LOG_ALLOW)
-			return -EINVAL;
+	if (!seccomp_actions_logged_from_names(&actions_logged, table.data))
+		return -EINVAL;
 
-		seccomp_actions_logged = actions_logged;
-	}
+	if (actions_logged & SECCOMP_LOG_ALLOW)
+		return -EINVAL;
 
+	seccomp_actions_logged = actions_logged;
 	return 0;
 }
 
+static int seccomp_actions_logged_handler(struct ctl_table *ro_table, int write,
+					  void __user *buffer, size_t *lenp,
+					  loff_t *ppos)
+{
+	if (write)
+		return write_actions_logged(ro_table, buffer, lenp, ppos);
+	else
+		return read_actions_logged(ro_table, buffer, lenp, ppos);
+}
+
 static struct ctl_path seccomp_sysctl_path[] = {
 	{ .procname = "kernel", },
 	{ .procname = "seccomp", },