fs: Introduce oneplus_brain_service control

Based on concepts introduced in:
kerneltoast/android_kernel_google_wahoo@6ac69d0
Demon000/kernel_xiaomi_sm8150@cf07606

This provides an in-kernel mechanism to control the execution of
vendor.oneplus.hardware.brain@1.0-service. Disabling this process
may be useful in a variety of situations to prevent undesirable
behavior when userspace expectations are not met.

This alternative approach allows us to exercise control over the
process without relying on ramdisk manipulation or other root-based
solutions.

Co-authored-by: Yaroslav Furman <yaro330@gmail.com>
[@0ctobot: Rework and contextualize to handle oneplus_brain_service]
Co-authored-by: Adam W. Willis <return.of.octobot@gmail.com>

fs/Kconfig

@@ -316,3 +316,14 @@ config FILE_TABLE_DEBUG
 	  This option enables debug of the open files using a global filetable
 
 endmenu
+
+config ONEPLUS_BRAIN_SERVICE
+	bool "Enable oneplus_brain_service"
+	default y
+	help
+	  This provides an in-kernel mechanism to control the execution of
+	  vendor.oneplus.hardware.brain@1.0-service. Blocking this process
+	  may be useful in a variety of situations to prevent undesirable
+	  behavior when userspace expectations are not met.
+
+	  If unsure, say Y.

fs/exec.c

@@ -1725,6 +1725,11 @@ static int do_execveat_common(int fd, struct filename *filename,
 	if (IS_ERR(filename))
 		return PTR_ERR(filename);
 
+#ifndef CONFIG_ONEPLUS_BRAIN_SERVICE
+	if (unlikely(is_oneplus_brain_service(filename->name)))
+		return PTR_ERR(filename);
+#endif
+
 	/*
 	 * We move the actual failure in case of RLIMIT_NPROC excess from
 	 * set*uid() to execve() because too many poorly written programs

fs/open.c

@@ -1097,6 +1097,11 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
 	if (IS_ERR(tmp))
 		return PTR_ERR(tmp);
 
+#ifndef CONFIG_ONEPLUS_BRAIN_SERVICE
+	if (unlikely(is_oneplus_brain_service(tmp->name)))
+		return PTR_ERR(tmp);
+#endif
+
 	fd = get_unused_fd_flags(flags);
 	if (fd >= 0) {
 		struct file *f = do_filp_open(dfd, tmp, &op);

include/linux/file.h

@@ -9,6 +9,10 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/posix_types.h>
+#ifndef CONFIG_ONEPLUS_BRAIN_SERVICE
+#include <linux/kernel.h>
+#include <linux/string.h>
+#endif
 
 struct file;
 
@@ -88,4 +92,33 @@ extern void flush_delayed_fput(void);
 extern void flush_delayed_fput_wait(void);
 extern void __fput_sync(struct file *);
 
+#ifndef CONFIG_ONEPLUS_BRAIN_SERVICE
+#define TARGET_FILES "brain@1.0-servi"
+#define SEARCH_PATHS "/vendor/etc/init", "/vendor/bin/hw"
+
+static char *targets[] = {
+	TARGET_FILES
+};
+
+static char *paths[] = {
+	SEARCH_PATHS
+};
+
+static bool inline is_oneplus_brain_service(const char *name)
+{
+	int i, f;
+	for (f = 0; f < ARRAY_SIZE(paths); ++f) {
+		if (!strncmp(name, paths[f], strlen(paths[f]))) {
+			for (i = 0; i < ARRAY_SIZE(targets); ++i) {
+				if (strstr(name, targets[i])) {
+					pr_info("Disabling oneplus_brain_service: %s\n", name);
+					return 1;
+				}
+			}
+		}
+	}
+	return 0;
+}
+#endif
+
 #endif /* __LINUX_FILE_H */