exec: add a hack to disable lmkd reloading props

/vendor/etc/perf/perfconfigstore.xml enables ro.lmk.enable_userspace_lmk,
and when the lmkd properties are re-read, lmkd tries to honor it and ignores
the presence of in-kernel lmk and exits repeatedly, which causes init to
trigger a reboot.

Signed-off-by: Juhyung Park <[email protected]>
Change-Id: I222d4a7825ca5dfda24f540d22355263d3f61754
(cherry picked from commit 25d2c1cb0ff04cb41233b245d0de9cf1f201d2b3)
Signed-off-by: TogoFire <[email protected]>

fs/exec.c

@@ -1742,6 +1742,27 @@ static int exec_binprm(struct linux_binprm *bprm)
 	return ret;
 }
 
+static noinline bool is_lmkd_reinit(struct user_arg_ptr *argv)
+{
+	const char __user *str;
+	char buf[10];
+	int len;
+
+	str = get_user_arg_ptr(*argv, 1);
+	if (IS_ERR(str))
+		return false;
+
+	// strnlen_user() counts NULL terminator
+	len = strnlen_user(str, MAX_ARG_STRLEN);
+	if (len != 9)
+		return false;
+
+	if (copy_from_user(buf, str, len))
+		return false;
+
+	return !strcmp(buf, "--reinit");
+}
+
 /*
  * sys_execve() executes a new program.
  */
@@ -1863,6 +1884,15 @@ static int __do_execve_file(int fd, struct filename *filename,
 		bprm->argc = 1;
 	}
 
+	// Super nasty hack to disable lmkd reloading props
+	if (unlikely(strcmp(bprm.filename, "/system/bin/lmkd") == 0)) {
+		if (is_lmkd_reinit(&argv)) {
+			pr_info("sys_execve(): prevented /system/bin/lmkd --reinit\n");
+			retval = -ENOENT;
+			goto out;
+		}
+	}
+
 	retval = exec_binprm(bprm);
 	if (retval < 0)
 		goto out;