From e419a79329819ee49c184d29acf626f1b2599537 Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn@google.com>
Date: Wed, 6 Mar 2019 15:18:46 -0800
Subject: [PATCH] ueventd: populate /dev/block/mapper link

Since DM_NAME= is not sent (delete bug) or interpreted with ueventd
message, instead probe /sys/devices/virtual/block/dm-X/dm/name when
instantiating.  Cache the value for later delete.

By creating the /dev/block/mapper/<name> nodes, this will give
selabel_lookup_best_match an alias to hang its hat on so that the
associated /dev/block/dm-X nodes will be suitably labelled and
differentiated.

NB: For Android, the deletion of the nodes will only happen in the
    context of fastbootd, update_engine and gsid; otherwise the links
    and properties created can be considered set-once and persistent.

Test: manual inspect /dev/block/mapper/ links
Bug: 124072565
Change-Id: I6d9e467970dfdad7b67754ad61084964251eb05f
---
 init/devices.cpp | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/init/devices.cpp b/init/devices.cpp
index 1a77ba19d..159c75e03 100644
--- a/init/devices.cpp
+++ b/init/devices.cpp
@@ -21,8 +21,14 @@
 #include <sys/sysmacros.h>
 #include <unistd.h>
 
+#include <chrono>
+#include <map>
 #include <memory>
+#include <string>
+#include <thread>
 
+#include <android-base/chrono_utils.h>
+#include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
@@ -37,12 +43,16 @@
 #error "Do not include init.h in files used by ueventd; it will expose init's globals"
 #endif
 
+using namespace std::chrono_literals;
+
 using android::base::Basename;
 using android::base::Dirname;
+using android::base::ReadFileToString;
 using android::base::Readlink;
 using android::base::Realpath;
 using android::base::StartsWith;
 using android::base::StringPrintf;
+using android::base::Trim;
 
 namespace android {
 namespace init {
@@ -101,6 +111,31 @@ static bool FindVbdDevicePrefix(const std::string& path, std::string* result) {
     return true;
 }
 
+// Given a path that may start with a virtual dm block device, populate
+// the supplied buffer with the dm module's instantiated name.
+// If it doesn't start with a virtual block device, or there is some
+// error, return false.
+static bool FindDmDevicePartition(const std::string& path, std::string* result) {
+    result->clear();
+    if (!StartsWith(path, "/devices/virtual/block/dm-")) return false;
+    if (getpid() == 1) return false;  // first_stage_init has no sepolicy needs
+
+    static std::map<std::string, std::string> cache;
+    // wait_for_file will not work, the content is also delayed ...
+    for (android::base::Timer t; t.duration() < 200ms; std::this_thread::sleep_for(10ms)) {
+        if (ReadFileToString("/sys" + path + "/dm/name", result) && !result->empty()) {
+            // Got it, set cache with result, when node arrives
+            cache[path] = *result = Trim(*result);
+            return true;
+        }
+    }
+    auto it = cache.find(path);
+    if ((it == cache.end()) || (it->second.empty())) return false;
+    // Return cached results, when node goes away
+    *result = it->second;
+    return true;
+}
+
 Permissions::Permissions(const std::string& name, mode_t perm, uid_t uid, gid_t gid)
     : name_(name), perm_(perm), uid_(uid), gid_(gid), prefix_(false), wildcard_(false) {
     // Set 'prefix_' or 'wildcard_' based on the below cases:
@@ -293,6 +328,7 @@ void SanitizePartitionName(std::string* string) {
 std::vector<std::string> DeviceHandler::GetBlockDeviceSymlinks(const Uevent& uevent) const {
     std::string device;
     std::string type;
+    std::string partition;
 
     if (FindPlatformDevice(uevent.path, &device)) {
         // Skip /devices/platform or /devices/ if present
@@ -310,6 +346,8 @@ std::vector<std::string> DeviceHandler::GetBlockDeviceSymlinks(const Uevent& uev
         type = "pci";
     } else if (FindVbdDevicePrefix(uevent.path, &device)) {
         type = "vbd";
+    } else if (FindDmDevicePartition(uevent.path, &partition)) {
+        return {"/dev/block/mapper/" + partition};
     } else {
         return {};
     }