pwn2python

re::re::re::re::
http://bugs.python.org/issue27254


<+16>:	movsxd rdx,DWORD PTR [rbx+0x8]
<+20>:	lea    eax,[rdx+rbp*1]

newSize = length ($rdx) + dsPtr->length ($rbp)
gdb > print /x $rbp
$5 = 0xfffff
gdb > print /x $rdx
$6 = 0x100000

newsize = 0xfffff+0x100000 = 0x1fffff

<Tcl_DStringAppend+23>  cmp    eax,DWORD PTR [rbx+0xc] 		 ← $pc
<Tcl_DStringAppend+26>  jl     0x7ffff6194e38 <Tcl_DStringAppend+104>

newSize ($eax) >= dsPtr->spaceAvl

gdb > print /x $eax
$7 = 0x1fffff

gdb > x/x $rbx+0xc
0x7fffffffd0cc:	0x001ffffe

condition: 0x1fffff >= 0x001ffffe = True

	if (newSize >= dsPtr->spaceAvl) {
		<Tcl_DStringAppend+31>  lea    esi,[rax+rax*1] ; magic compiler optimization :) (newSize(0x1fffff)*2)
		/*							*/
		dsPtr->spaceAvl = newSize * 2;
		gdb > print /x $rax
		$4 = 0x1fffff
		$esi = 0x1fffff+0x1fffff (newSize(0x1fffff)*2) = 0x3ffffe
		/*							*/

		=> <+34>:	lea    rax,[rbx+0x10]
		   <+38>:	mov    DWORD PTR [rbx+0xc],esi
		   <+41>:	cmp    rdi,rax ; $rax = dsPtr->staticSpace and $rdi = dsPtr->string
		   <+44>:	je     0x7ffff6194e50 <Tcl_DStringAppend+128>

		condition : dsPtr->string == dsPtr->staticSpace = False then jump to '<Tcl_DStringAppend+46>  call   0x7ffff60c2040 <Tcl_Realloc>'

	        if (dsPtr->string == dsPtr->staticSpace) {
			char *newString = ckalloc(dsPtr->spaceAvl);
            		memcpy(newString, dsPtr->string, (size_t) dsPtr->length);
			dsPtr->string = newString;
		}
		else {
			<Tcl_DStringAppend+46>  call   0x7ffff60c2040 <Tcl_Realloc>
			$rsi = 0x3ffffe
			$rdi = 0x7ffff333e020
			dsPtr->string = ckrealloc(dsPtr->string = 0x7ffff333e020, dsPtr->spaceAvl = 0x3ffffe);
		}
	}


disassemble:
		 <Tcl_DStringAppend+58>  lea    rdi,[rax+rdx*1] 	; dsPtr->string + dsPtr->length
		 <Tcl_DStringAppend+62>  mov    rsi,r12			; bytes
		 <Tcl_DStringAppend+65>  movsxd rdx,ebp			; length
		 <Tcl_DStringAppend+68>  call   0x7ffff60a25c0 <memcpy@plt>
		 memcpy(dsPtr->string + dsPtr->length, bytes, length);


ASAN ;;

=================================================================
==27988==ERROR: AddressSanitizer: heap-use-after-free on address 0x7f4e6ba64810 at pc 0x4665ea bp 0x7fff89a4ab80 sp 0x7fff89a4a340
READ of size 1048575 at 0x7f4e6ba64810 thread T0
==27988==WARNING: Trying to symbolize code, but external symbolizer is not initialized!
    #0 0x4665e9 (/home/eminus/Downloads/Python-2.7.11/python+0x4665e9)
    #1 0x7f4e6f0a3e18 (/usr/lib/x86_64-linux-gnu/libtcl8.6.so+0x116e18)
    #2 0x7f4e6f38744e (/usr/lib/x86_64-linux-gnu/libtk8.6.so+0x6244e)
    #3 0x7f4e6f6b6e4c (/home/eminus/Downloads/Python-2.7.11/build/lib.linux-x86_64-2.7/_tkinter.so+0x19e4c)
    #4 0x7f4e6f6a7fc5 (/home/eminus/Downloads/Python-2.7.11/build/lib.linux-x86_64-2.7/_tkinter.so+0xafc5)
    #5 0x5e1813 (/home/eminus/Downloads/Python-2.7.11/python+0x5e1813)
    #6 0x5d319c (/home/eminus/Downloads/Python-2.7.11/python+0x5d319c)
    #7 0x721353 (/home/eminus/Downloads/Python-2.7.11/python+0x721353)
    #8 0x4acb2a (/home/eminus/Downloads/Python-2.7.11/python+0x4acb2a)
    #9 0x4b6c62 (/home/eminus/Downloads/Python-2.7.11/python+0x4b6c62)
    #10 0x4acb2a (/home/eminus/Downloads/Python-2.7.11/python+0x4acb2a)
    #11 0x5f0823 (/home/eminus/Downloads/Python-2.7.11/python+0x5f0823)
    #12 0x4b0a08 (/home/eminus/Downloads/Python-2.7.11/python+0x4b0a08)
    #13 0x4acb2a (/home/eminus/Downloads/Python-2.7.11/python+0x4acb2a)
    #14 0x5e2d19 (/home/eminus/Downloads/Python-2.7.11/python+0x5e2d19)
    #15 0x5d319c (/home/eminus/Downloads/Python-2.7.11/python+0x5d319c)
    #16 0x5d2041 (/home/eminus/Downloads/Python-2.7.11/python+0x5d2041)
    #17 0x660980 (/home/eminus/Downloads/Python-2.7.11/python+0x660980)
    #18 0x65fc8a (/home/eminus/Downloads/Python-2.7.11/python+0x65fc8a)
    #19 0x48e46c (/home/eminus/Downloads/Python-2.7.11/python+0x48e46c)
    #20 0x7f4e72389ec4 (/lib/x86_64-linux-gnu/libc.so.6+0x21ec4)
    #21 0x48c5bc (/home/eminus/Downloads/Python-2.7.11/python+0x48c5bc)

0x7f4e6ba64810 is located 16 bytes inside of 2097166-byte region [0x7f4e6ba64800,0x7f4e6bc6480e)
freed by thread T0 here:
    #0 0x4766d3 (/home/eminus/Downloads/Python-2.7.11/python+0x4766d3)
    #1 0x7f4e6f09b52d (/usr/lib/x86_64-linux-gnu/libtcl8.6.so+0x10e52d)

previously allocated by thread T0 here:
    #0 0x4764d9 (/home/eminus/Downloads/Python-2.7.11/python+0x4764d9)
    #1 0x7f4e6f09b0cc (/usr/lib/x86_64-linux-gnu/libtcl8.6.so+0x10e0cc)

SUMMARY: AddressSanitizer: heap-use-after-free ??:0 ??
Shadow bytes around the buggy address:
  0x0fea4d7448b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0fea4d7448c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0fea4d7448d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0fea4d7448e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0fea4d7448f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0fea4d744900: fd fd[fd]fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0fea4d744910: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0fea4d744920: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0fea4d744930: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0fea4d744940: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0fea4d744950: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:     fa
  Heap right redzone:    fb
  Freed heap region:     fd
  Stack left redzone:    f1
  Stack mid redzone:     f2
  Stack right redzone:   f3
  Stack partial redzone: f4
  Stack after return:    f5
  Stack use after scope: f8
  Global redzone:        f9
  Global init order:     f6
  Poisoned by user:      f7
  ASan internal:         fe
==27988==ABORTING


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