1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
#include "core/convar/convar.h"
#include "engine/r2engine.h"
#include "shared/exploit_fixes/ns_limits.h"
#include "masterserver/masterserver.h"
#include <string>
#include <thread>
#include <bcrypt.h>
AUTOHOOK_INIT()
static ConVar* Cvar_net_debug_atlas_packet;
static ConVar* Cvar_net_debug_atlas_packet_insecure;
static BCRYPT_ALG_HANDLE HMACSHA256;
constexpr size_t HMACSHA256_LEN = 256 / 8;
static bool InitHMACSHA256()
{
NTSTATUS status;
DWORD hashLength = 0;
ULONG hashLengthSz = 0;
if ((status = BCryptOpenAlgorithmProvider(&HMACSHA256, BCRYPT_SHA256_ALGORITHM, NULL, BCRYPT_ALG_HANDLE_HMAC_FLAG)))
{
spdlog::error("failed to initialize HMAC-SHA256: BCryptOpenAlgorithmProvider: error 0x{:08X}", (ULONG)status);
return false;
}
if ((status = BCryptGetProperty(HMACSHA256, BCRYPT_HASH_LENGTH, (PUCHAR)&hashLength, sizeof(hashLength), &hashLengthSz, 0)))
{
spdlog::error("failed to initialize HMAC-SHA256: BCryptGetProperty(BCRYPT_HASH_LENGTH): error 0x{:08X}", (ULONG)status);
return false;
}
if (hashLength != HMACSHA256_LEN)
{
spdlog::error("failed to initialize HMAC-SHA256: BCryptGetProperty(BCRYPT_HASH_LENGTH): unexpected value {}", hashLength);
return false;
}
return true;
}
// compare the HMAC-SHA256(data, key) against sig (note: all strings are treated as raw binary data)
static bool VerifyHMACSHA256(std::string key, std::string sig, std::string data)
{
uint8_t invalid = 1;
char hash[HMACSHA256_LEN];
NTSTATUS status;
BCRYPT_HASH_HANDLE h = NULL;
if ((status = BCryptCreateHash(HMACSHA256, &h, NULL, 0, (PUCHAR)key.c_str(), (ULONG)key.length(), 0)))
{
spdlog::error("failed to verify HMAC-SHA256: BCryptCreateHash: error 0x{:08X}", (ULONG)status);
goto cleanup;
}
if ((status = BCryptHashData(h, (PUCHAR)data.c_str(), (ULONG)data.length(), 0)))
{
spdlog::error("failed to verify HMAC-SHA256: BCryptHashData: error 0x{:08X}", (ULONG)status);
goto cleanup;
}
if ((status = BCryptFinishHash(h, (PUCHAR)&hash, (ULONG)sizeof(hash), 0)))
{
spdlog::error("failed to verify HMAC-SHA256: BCryptFinishHash: error 0x{:08X}", (ULONG)status);
goto cleanup;
}
// constant-time compare
if (sig.length() == sizeof(hash))
{
invalid = 0;
for (size_t i = 0; i < sizeof(hash); i++)
invalid |= (uint8_t)(sig[i]) ^ (uint8_t)(hash[i]);
}
cleanup:
if (h)
BCryptDestroyHash(h);
return !invalid;
}
// v1 HMACSHA256-signed masterserver request (HMAC-SHA256(JSONData, MasterServerToken) + JSONData)
static void ProcessAtlasConnectionlessPacketSigreq1(netpacket_t* packet, bool dbg, std::string pType, std::string pData)
{
if (pData.length() < HMACSHA256_LEN)
{
if (dbg)
spdlog::warn("ignoring Atlas connectionless packet (size={} type={}): invalid: too short for signature", packet->size, pType);
return;
}
std::string pSig; // is binary data, not actually an ASCII string
pSig = pData.substr(0, HMACSHA256_LEN);
pData = pData.substr(HMACSHA256_LEN);
if (!g_pMasterServerManager || !g_pMasterServerManager->m_sOwnServerAuthToken[0])
{
if (dbg)
spdlog::warn(
"ignoring Atlas connectionless packet (size={} type={}): invalid (data={}): no masterserver token yet",
packet->size,
pType,
pData);
return;
}
if (!VerifyHMACSHA256(std::string(g_pMasterServerManager->m_sOwnServerAuthToken), pSig, pData))
{
if (!Cvar_net_debug_atlas_packet_insecure->GetBool())
{
if (dbg)
spdlog::warn(
"ignoring Atlas connectionless packet (size={} type={}): invalid: invalid signature (key={})",
packet->size,
pType,
std::string(g_pMasterServerManager->m_sOwnServerAuthToken));
return;
}
spdlog::warn(
"processing Atlas connectionless packet (size={} type={}) with invalid signature due to net_debug_atlas_packet_insecure",
packet->size,
pType);
}
if (dbg)
spdlog::info("got Atlas connectionless packet (size={} type={} data={})", packet->size, pType, pData);
std::thread t(&MasterServerManager::ProcessConnectionlessPacketSigreq1, g_pMasterServerManager, pData);
t.detach();
return;
}
static void ProcessAtlasConnectionlessPacket(netpacket_t* packet)
{
bool dbg = Cvar_net_debug_atlas_packet->GetBool();
// extract kind, null-terminated type, data
std::string pType, pData;
for (int i = 5; i < packet->size; i++)
{
if (packet->data[i] == '\x00')
{
pType.assign((char*)(&packet->data[5]), (size_t)(i - 5));
if (i + 1 < packet->size)
pData.assign((char*)(&packet->data[i + 1]), (size_t)(packet->size - i - 1));
break;
}
}
// note: all Atlas connectionless packets should be idempotent so multiple attempts can be made to mitigate packet loss
// note: all long-running Atlas connectionless packet handlers should be started in a new thread (with copies of the data) to avoid
// blocking networking
// v1 HMACSHA256-signed masterserver request
if (pType == "sigreq1")
{
ProcessAtlasConnectionlessPacketSigreq1(packet, dbg, pType, pData);
return;
}
if (dbg)
spdlog::warn("ignoring Atlas connectionless packet (size={} type={}): unknown type", packet->size, pType);
return;
}
AUTOHOOK(ProcessConnectionlessPacket, engine.dll + 0x117800, bool, , (void* a1, netpacket_t* packet))
{
// packet->data consists of 0xFFFFFFFF (int32 -1) to indicate packets aren't split, followed by a header consisting of a single
// character, which is used to uniquely identify the packet kind. Most kinds follow this with a null-terminated string payload
// then an arbitrary amoount of data.
// T (no rate limits since we authenticate packets before doing anything expensive)
if (4 < packet->size && packet->data[4] == 'T')
{
ProcessAtlasConnectionlessPacket(packet);
return false;
}
// check rate limits for the original unconnected packets
if (!g_pServerLimits->CheckConnectionlessPacketLimits(packet))
return false;
// A, H, I, N
return ProcessConnectionlessPacket(a1, packet);
}
ON_DLL_LOAD_RELIESON("engine.dll", ServerNetHooks, ConVar, (CModule module))
{
AUTOHOOK_DISPATCH_MODULE(engine.dll)
if (!InitHMACSHA256())
throw std::runtime_error("failed to initialize bcrypt");
if (!VerifyHMACSHA256(
"test",
"\x88\xcd\x21\x08\xb5\x34\x7d\x97\x3c\xf3\x9c\xdf\x90\x53\xd7\xdd\x42\x70\x48\x76\xd8\xc9\xa9\xbd\x8e\x2d\x16\x82\x59\xd3\xdd"
"\xf7",
"test"))
throw std::runtime_error("bcrypt HMAC-SHA256 is broken");
Cvar_net_debug_atlas_packet = new ConVar(
"net_debug_atlas_packet",
"0",
FCVAR_NONE,
"Whether to log detailed debugging information for Atlas connectionless packets (warning: this allows unlimited amounts of "
"arbitrary data to be logged)");
Cvar_net_debug_atlas_packet_insecure = new ConVar(
"net_debug_atlas_packet_insecure",
"0",
FCVAR_NONE,
"Whether to disable signature verification for Atlas connectionless packets (DANGEROUS: this allows anyone to impersonate Atlas)");
}
|
