From ac39cb00a04c571699df695ce0d144d8cb386f35 Mon Sep 17 00:00:00 2001
From: Pierre-Hugues Husson <phh@phh.me>
Date: Sat, 19 Feb 2022 08:20:25 -0500
Subject: [PATCH] Add new mechanism to fake vendor props on a per-process basis

This reads debug.phh.props.<process name>. If its value is "vendor",
then ro.product.device/ro.product.manufacturer is read from vendor
---
 libc/system_properties/system_properties.cpp | 87 +++++++++++++++++++-
 1 file changed, 85 insertions(+), 2 deletions(-)

diff --git a/libc/system_properties/system_properties.cpp b/libc/system_properties/system_properties.cpp
index 9dd5e35ce..886bef127 100644
--- a/libc/system_properties/system_properties.cpp
+++ b/libc/system_properties/system_properties.cpp
@@ -36,6 +36,8 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <string.h>
+#include <fcntl.h>
 
 #include <new>
 
@@ -53,6 +55,85 @@
 #define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
 #define APPCOMPAT_PREFIX "ro.appcompat_override."
 
+static char comm[128];
+static bool self_ok = false;
+static char comm_override[PROP_VALUE_MAX];
+
+static void read_self() {
+  //NB: Not atomic, but should be good enough, there is no possible corruption from concurrency
+  if(self_ok) return;
+  self_ok = true;
+
+  char cmdline[128];
+  int fd = open("/proc/self/cmdline", O_RDONLY);
+  if(fd<0) return;
+  read(fd, cmdline, sizeof(cmdline)-1);
+  for(unsigned i=0; i<sizeof(cmdline); i++)
+    if(cmdline[i] == '\n')
+      cmdline[i] = 0;
+  close(fd);
+
+  // Truncate to last /, we don't want `/` in the prop
+  const char *c = strrchr(cmdline, '/');
+  if (c != nullptr) {
+      c = c+1;
+  } else {
+      c = cmdline;
+  }
+  // Take only the last 16 bytes (prop names max is 32)
+  if(strlen(c) < 15) {
+      strcpy(comm, c);
+  } else {
+      strcpy(comm, c + strlen(c) - 15);
+  }
+
+
+  //That's calling ourselves but that's fine because we already have self_ok = true
+  char propName[PROP_NAME_MAX];
+  memset(propName, 0, PROP_NAME_MAX);
+  strncpy(propName, "debug.phh.props.", PROP_NAME_MAX - 1);
+  strncat(propName, comm, PROP_NAME_MAX - strlen(propName) - 1);
+
+  //async_safe_format_log(ANDROID_LOG_WARN, "libc", "Reading debug prop %s", propName);
+  __system_property_get(propName, comm_override);
+}
+
+static const char* redirectToProp(const char *name) {
+  read_self();
+  /*if(strstr(name, "ro.keymaster") != nullptr || strstr(name, "security_patch") != nullptr || strstr(name, "release") != nullptr) {
+    async_safe_format_log(ANDROID_LOG_WARN, "libc", "Process/comm %s/%s is reading %s", comm, comm_override, name);
+  }*/
+  if(strcmp(comm_override, "vendor") == 0) {
+    if(strcmp(name, "ro.product.device") == 0) {
+      return "ro.product.vendor.device";
+    }
+    if(strcmp(name, "ro.product.manufacturer") == 0) {
+      return "ro.product.vendor.manufacturer";
+    }
+  }
+  if(strcmp(comm_override, "keymaster") == 0) {
+    if(strcmp(name, "ro.product.model") == 0) {
+      return "ro.keymaster.mod";
+    }
+    if(strcmp(name, "ro.product.brand") == 0) {
+      return "ro.keymaster.brn";
+    }
+    if(strcmp(name, "ro.build.version.release") == 0) {
+      return "ro.keymaster.xxx.release";
+    }
+    if(strcmp(name, "ro.build.version.security_patch") == 0) {
+      return "ro.keymaster.xxx.security_patch";
+    }
+    if(strcmp(name, "ro.boot.vbmeta.device_state") == 0) {
+      return "ro.keymaster.xxx.vbmeta_state";
+    }
+    if(strcmp(name, "ro.boot.verifiedbootstate") == 0) {
+      return "ro.keymaster.xxx.verifiedbootstate";
+    }
+  }
+  return name;
+}
+
 static bool is_dir(const char* pathname) {
   struct stat info;
   if (stat(pathname, &info) == -1) {
@@ -156,17 +237,19 @@ uint32_t SystemProperties::AreaSerial() {
 }
 
 const prop_info* SystemProperties::Find(const char* name) {
+  const char* newName = redirectToProp(name);
+
   if (!initialized_) {
     return nullptr;
   }
 
-  prop_area* pa = contexts_->GetPropAreaForName(name);
+  prop_area* pa = contexts_->GetPropAreaForName(newName);
   if (!pa) {
     async_safe_format_log(ANDROID_LOG_WARN, "libc", "Access denied finding property \"%s\"", name);
     return nullptr;
   }
 
-  return pa->find(name);
+  return pa->find(newName);
 }
 
 static bool is_appcompat_override(const char* name) {
-- 
2.34.1