From 997d738dda66df669837cb27b39e09ed12316e47 Mon Sep 17 00:00:00 2001
From: Nathan Huckleberry <nhuck@google.com>
Date: Fri, 21 Oct 2022 20:55:49 +0000
Subject: [PATCH] Expose system property for dm-verity check_at_most_once

Allow us to check if check_at_most_once is set for any partitions.

This property should be false for any device with a reasonable amount of
RAM and a modern CPU. Enabling check_at_most_once violates AVB best
practices, it should only be allowed on performance limited devices.

Bug: 253033920
Test: Ensure that avbHashtreeNotUsingSha1 CTS test still passes
    and that partition.system.verified.check_at_most_once is set.
Change-Id: I8174adf81111cc0df547ea01f81b0dfaca32631f
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
---
 fs_mgr/fs_mgr.cpp       | 28 +++++++---------------------
 fs_mgr/include/fs_mgr.h |  2 ++
 init/builtins.cpp       |  2 ++
 3 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/fs_mgr/fs_mgr.cpp b/fs_mgr/fs_mgr.cpp
index 27137a298..1c1ab48d4 100644
--- a/fs_mgr/fs_mgr.cpp
+++ b/fs_mgr/fs_mgr.cpp
@@ -2191,36 +2191,22 @@ std::optional<HashtreeInfo> fs_mgr_get_hashtree_info(const android::fs_mgr::Fsta
         std::vector<std::string> tokens = android::base::Split(target.data, " \t\r\n");
         if (tokens[0] != "0" && tokens[0] != "1") {
             LOG(WARNING) << "Unrecognized device mapper version in " << target.data;
-            return {};
         }
 
         // Hashtree algorithm & root digest are the 8th & 9th token in the output.
-        return HashtreeInfo{.algorithm = android::base::Trim(tokens[7]),
-                            .root_digest = android::base::Trim(tokens[8])};
+        return HashtreeInfo{
+                .algorithm = android::base::Trim(tokens[7]),
+                .root_digest = android::base::Trim(tokens[8]),
+                .check_at_most_once = target.data.find("check_at_most_once") != std::string::npos};
     }
 
     return {};
 }
 
 bool fs_mgr_verity_is_check_at_most_once(const android::fs_mgr::FstabEntry& entry) {
-    if (!entry.fs_mgr_flags.avb) {
-        return false;
-    }
-
-    DeviceMapper& dm = DeviceMapper::Instance();
-    std::string device = GetVerityDeviceName(entry);
-
-    std::vector<DeviceMapper::TargetInfo> table;
-    if (dm.GetState(device) == DmDeviceState::INVALID || !dm.GetTableInfo(device, &table)) {
-        return false;
-    }
-    for (const auto& target : table) {
-        if (strcmp(target.spec.target_type, "verity") == 0 &&
-            target.data.find("check_at_most_once") != std::string::npos) {
-            return true;
-        }
-    }
-    return false;
+    auto hashtree_info = fs_mgr_get_hashtree_info(entry);
+    if (!hashtree_info) return false;
+    return hashtree_info->check_at_most_once;
 }
 
 std::string fs_mgr_get_super_partition_name(int slot) {
diff --git a/fs_mgr/include/fs_mgr.h b/fs_mgr/include/fs_mgr.h
index 29a5e60e6..43de6d84c 100644
--- a/fs_mgr/include/fs_mgr.h
+++ b/fs_mgr/include/fs_mgr.h
@@ -71,6 +71,8 @@ struct HashtreeInfo {
     std::string algorithm;
     // The root digest of the merkle tree.
     std::string root_digest;
+    // If check_at_most_once is enabled.
+    bool check_at_most_once;
 };
 
 // fs_mgr_mount_all() updates fstab entries that reference device-mapper.
diff --git a/init/builtins.cpp b/init/builtins.cpp
index c8cb25300..7cb8b1149 100644
--- a/init/builtins.cpp
+++ b/init/builtins.cpp
@@ -879,6 +879,8 @@ static Result<void> do_verity_update_state(const BuiltinArguments& args) {
             SetProperty("partition." + partition + ".verified.hash_alg", hashtree_info->algorithm);
             SetProperty("partition." + partition + ".verified.root_digest",
                         hashtree_info->root_digest);
+            SetProperty("partition." + partition + ".verified.check_at_most_once",
+                        hashtree_info->check_at_most_once ? "1" : "0");
         }
     }