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Gracia Final Teleport Crash Partial Fix


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There's a race condition error in engine.dll:

 

engine.dll:00CE80AA lea     eax, [eax+edx*4]
engine.dll:00CE80AD cmp     dword ptr [eax+10h], 0  <----- now it's not 0, so it won't jump on the next line
engine.dll:00CE80B1 jz      0CE80C8h     -- meanwhile some other thread sets dword ptr [eax+10h] to 0 --
engine.dll:00CE80B3 mov     ecx, [eax+10h]    <----- so now we have ecx == 0
engine.dll:00CE80B6 mov     ecx, [ecx+1Ch]    <----- read dword ptr [0+1ch] -> CRASH
engine.dll:00CE80B9 test    ecx, 0x4000000
engine.dll:00CE80BF jnz     short loc_CE80C8
engine.dll:00CE80C1 mov     dword ptr [eax+10h], 0
 
It can be fixed this way:
 
engine.dll:00CE80AA lea     eax, [eax+edx*4]
engine.dll:00CE80AD mov     ecx, [eax+10h]   <----- we copy that value from memory
engine.dll:00CE80B0 jecxz   0CE80C8h          <----- and compare it this way - jecxz is a nice instruction :)
engine.dll:00CE80B2 mov     ecx, [ecx+1ch]    <----- even if some other thread resets dword ptr [eax+10h], we have still copy in ecx
engine.dll:00CE80B5 test    ecx, 0x4000000
engine.dll:00CE80BB jne     0CE80C8h
engine.dll:00CE80BD nop
engine.dll:00CE80BE nop           <----- we saved 4 bytes :)
engine.dll:00CE80BF nop
engine.dll:00CE80C0 nop
engine.dll:00CE80C1 mov     dword ptr [eax+10h], 0
 
There are two occurrences of this bug in engine.dll, to fix them both replace following (in unpacked engine.dll ofc)
 
old: 83 78 10 00 74 15 8B 48 10 8B 49 1C F7 C1 00 00 00 04 75 07
new: 8B 48 10 E3 16 8B 49 1C F7 C1 00 00 00 04 75 0B 90 90 90 90
 
old: 83 78 10 00 74 13 8B 48 10 F7 41 1C 00 00 00 04 75 07
new: 8B 48 10 E3 14 F7 41 1C 00 00 00 04 75 0b 90 90 90 90
 
Enjoy ;)
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There's a race condition error in engine.dll:

 

engine.dll:00CE80AA lea     eax, [eax+edx*4]
engine.dll:00CE80AD cmp     dword ptr [eax+10h], 0  <----- now it's not 0, so it won't jump on the next line
engine.dll:00CE80B1 jz      0CE80C8h     -- meanwhile some other thread sets dword ptr [eax+10h] to 0 --
engine.dll:00CE80B3 mov     ecx, [eax+10h]    <----- so now we have ecx == 0
engine.dll:00CE80B6 mov     ecx, [ecx+1Ch]    <----- read dword ptr [0+1ch] -> CRASH
engine.dll:00CE80B9 test    ecx, 0x4000000
engine.dll:00CE80BF jnz     short loc_CE80C8
engine.dll:00CE80C1 mov     dword ptr [eax+10h], 0
 
It can be fixed this way:
 
engine.dll:00CE80AA lea     eax, [eax+edx*4]
engine.dll:00CE80AD mov     ecx, [eax+10h]   <----- we copy that value from memory
engine.dll:00CE80B0 jecxz   0CE80C8h          <----- and compare it this way - jecxz is a nice instruction :)
engine.dll:00CE80B2 mov     ecx, [ecx+1ch]    <----- even if some other thread resets dword ptr [eax+10h], we have still copy in ecx
engine.dll:00CE80B5 test    ecx, 0x4000000
engine.dll:00CE80BB jne     0CE80C8h
engine.dll:00CE80BD nop
engine.dll:00CE80BE nop           <----- we saved 4 bytes :)
engine.dll:00CE80BF nop
engine.dll:00CE80C0 nop
engine.dll:00CE80C1 mov     dword ptr [eax+10h], 0
 
There are two occurrences of this bug in engine.dll, to fix them both replace following (in unpacked engine.dll ofc)
 
old: 83 78 10 00 74 15 8B 48 10 8B 49 1C F7 C1 00 00 00 04 75 07
new: 8B 48 10 E3 16 8B 49 1C F7 C1 00 00 00 04 75 0B 90 90 90 90
 
old: 83 78 10 00 74 13 8B 48 10 F7 41 1C 00 00 00 04 75 07
new: 8B 48 10 E3 14 F7 41 1C 00 00 00 04 75 0b 90 90 90 90
 
Enjoy ;)

 

do you even know what that code is doing ? originaly , just setting to zero wouldnt explain the crash.

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do you even know what that code is doing ? originaly , just setting to zero wouldnt explain the crash.

 

Not in the global scope, but for example the first one is in UGameEngine::LoadMapThread.

They call something like

 

UObjectLoader *res = UObject::GetLoader(something);

if (res->var84h[something2]->var10h) {

    here they access res->var84h[something2]->var10h->var1c

    which is totally wrong if you don't have mutex here

}

 

so my fix does simply this:

 

void *someptr = res->var84h[something2]->var10h;

if (*someptr) {

    now i work with someptr which is copy

}

 

the best solution would be to add mutexes, but I don't have the source code :))

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Not in the global scope, but for example the first one is in UGameEngine::LoadMapThread.

They call something like

 

UObjectLoader *res = UObject::GetLoader(something);

if (res->var84h[something2]->var10h) {

    here they access res->var84h[something2]->var10h->var1c

    which is totally wrong if you don't have mutex here

}

 

so my fix does simply this:

 

void *someptr = res->var84h[something2]->var10h;

if (*someptr) {

    now i work with someptr which is copy

}

 

the best solution would be to add mutexes, but I don't have the source code :))

well thats acctualy explains better, a check if exist pattern 

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