[bug] crash while compiling sample (fasm v1.73.30)

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vityacv

Joined: 27 Oct 2012
Posts: 7

vityacv 12 Jul 2023, 06:41

stub64.asm:

Code:

format binary 
use64 
struct IMAGE_DOS_HEADER
e_magic rw 1 
e_cblp rw 1
e_cp rw 1
e_crlc rw 1
e_cparhdr rw 1 
e_minalloc rw 1
e_maxalloc rw 1
e_ss rw 1
e_sp rw 1
e_csum rw 1
e_ip rw 1
e_cs rw 1
e_lfarlc rw 1
e_ovno rw 1
e_res rw 4 
e_oemid rw 1 
e_oeminfo rw 1 
e_res2 rw 10 
e_lfanew rd 1
ends 

teste IMAGE_DOS_HEADER 'MZ',testq.size,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,testq.size 

testq:
mov rax,1 
align 4 
testq.size = $-teste

test64.asm:

Code:

format pe64 on 'stub64.bin' 
entry Main
Main: 
ret

results in

Code:

---------------------------                                                                                                             
fasm.exe - Application Error                                                                                                            
---------------------------                                                                                                             
The instruction at 0x0000000000419994 referenced memory at 0x0000000040B10000. The memory could not be written.                         
                                                                                                                                        
                                                                                                                                        
Click on OK to terminate the program                                                                                                    
---------------------------                                                                                                             
OK                                                                                                                                      
---------------------------

12 Jul 2023, 06:41

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 12 Jul 2023, 07:58

Your stub.asm does not assemble.

Code:

flat assembler  version 1.73.30  (16384 kilobytes memory)memory)
stub64.asm [3]:
struct IMAGE_DOS_HEADER
processed: struct IMAGE_DOS_HEADER
error: illegal instruction.

12 Jul 2023, 07:58

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 12 Jul 2023, 08:07

I changed stub64.asm to this:

Code:

format binary
use64
teste:  e_magic         db      'MZ'
        e_cblp          dw      testq.size
        e_cp            rw      1
        e_crlc          rw      1
        e_cparhdr       rw      1
        e_minalloc      rw      1
        e_maxalloc      rw      1
        e_ss            rw      1
        e_sp            rw      1
        e_csum          rw      1
        e_ip            rw      1
        e_cs            rw      1
        e_lfarlc        rw      1
        e_ovno          rw      1
        e_res           rw      1
        e_oemid         rw      1
        e_oeminfo       rw      1
        e_res2          rw      10
        e_lfanew        dd      testq.size

testq:
mov rax,1
align 4
testq.size = $-teste

Now I can reproduce your resutl:

Code:

flat assembler  version 1.73.30  (16384 kilobytes memory)
Segmentation fault (core dumped)

12 Jul 2023, 08:07

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 12 Jul 2023, 08:24

In formats.inc around line 742 we can add one line:

Code:

;...
        call    lseek
        movzx   ecx,word [esi+4]
        dec     ecx
js out_of_memory  ; <--- add this line
        shl     ecx,9
        movzx   edx,word [esi+2]
        test    edx,edx
        jnz     stub_header_size_ok
;...

Jumping to out_of_memory isn't really correct, but there is no dedicated error message to indicate a malformed stub file. At least it won't crash, it prints out of memory instead.

12 Jul 2023, 08:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20513
Location: In your JS exploiting you and your system

revolution 12 Jul 2023, 16:17

No crash in 1.73.31

Code:

flat assembler  version 1.73.31  (16384 kilobytes memory)
error: out of memory.

12 Jul 2023, 16:17

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