[solved] Incorrect memory allocation

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GREYSERGING

Joined: 03 Oct 2022
Posts: 4

GREYSERGING 03 Oct 2022, 09:05

Data section:

Code:

boundary db 8 dup (0)
header db 53 dup (0)
send_data dd ?
GetProcessHeapMem dd ?

At the beginning of the program, I allocate memory to the send_data variable

Code:

invoke GetProcessHeap
mov [GetProcessHeapMem],eax
invoke HeapAlloc,[GetProcessHeapMem],0,1024
mov [send_data],eax

Then I form a header to send the POST

Code:

invoke memcpy, header, header_no_boundary, 44
invoke memcpy, header + 44, boundary, 8

invoke memcpy, send_data, data1, 2
invoke memcpy, send_data + 2, boundary, 8
...

And I'm sending it

Code:

invoke HttpSendRequestA, [hora], header, 52, send_data, 110

The header itself is sent successfully, but send_data is not sent, I cannot allocate send_data fixed memory since the data can be either several kilobytes or hundreds of megobytes, but if I do so

Code:

send_data db 1024 dup (0)

Then everything went well, I suspect that the problem is in HeapAlloc, but I can't say for sure, so tell me what's the matter?

03 Oct 2022, 09:05

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20623
Location: In your JS exploiting you and your system

revolution 03 Oct 2022, 09:13

You are using send_data as both a buffer and a pointer.

Try something like this:

Code:

mov ebx.[send_data]
nvoke memcpy, ebx, data1, 2
nvoke memcpy, addr ebx+2, data1, 2
;...
invoke HttpSendRequestA, [hora], header, 52, [send_data], 110

03 Oct 2022, 09:13

GREYSERGING

Joined: 03 Oct 2022
Posts: 4

GREYSERGING 03 Oct 2022, 09:19

It didn't help, this is my complete code

Last edited by GREYSERGING on 03 Oct 2022, 09:27; edited 1 time in total

03 Oct 2022, 09:19

GREYSERGING

Joined: 03 Oct 2022
Posts: 4

GREYSERGING 03 Oct 2022, 09:27

Thank you, everything worked out, I initially misunderstood

03 Oct 2022, 09:27

Overclick

Joined: 11 Jul 2020
Posts: 670
Location: Ukraine

Overclick 03 Oct 2022, 14:00

You cannot be sure registers still keeping your data after winapi. Also memcpy uses some extra instructions you dont't really need to complete the task. Use movsb(w,d,q) instead.

Code:

macro   memcopy Dest_addr,Source_addr,len
        {
                mov     rdi,Dest_addr
                mov     rsi,Source_addr
                mov     rcx,len
                rep movsb
        }

Or even better

Code:

macro   memcopy Dest_addr,Source_addr,len
        {
                mov     rdi,Dest_addr
                mov     rsi,Source_addr
                mov     rcx,len
                shr     rcx,3
                rep movsq
                mov     rcx,len
                and     rcx,7
                rep movsb
        }

03 Oct 2022, 14:00

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20623
Location: In your JS exploiting you and your system

revolution 03 Oct 2022, 14:14

Overclick wrote:

You cannot be sure registers still keeping your data after winapi.

The Windows API calling standard (stdcall for 32-bit) is well documented.

EBX, EDI, ESI & EBP are all guaranteed to be preserved upon return.

03 Oct 2022, 14:14

GREYSERGING

Joined: 03 Oct 2022
Posts: 4

GREYSERGING 03 Oct 2022, 16:58

Thanks

03 Oct 2022, 16:58

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