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From: Christian Franke <Christian DOT Franke AT t-online DOT de>
Subject: Re: problem with i686-w64-mingw32-gcc -fstack-protector-all
To: cygwin AT cygwin DOT com
References: <CAD8GWsuRTR2asWX2zNnYJWj2EwbTVjqb=kx4kh2XxnO4OmW4jg AT mail DOT gmail DOT com>
Message-ID: <1d6ce5fb-ea05-b830-8096-98d839cc6e02@t-online.de>
Date: Wed, 4 Oct 2017 21:18:21 +0200
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Lee wrote:
> Maybe I'm just Doing It Wrong, but
>    gcc -fstack-protector-all
> seems to be working correctly &
>    i686-w64-mingw32-gcc -fstack-protector-all
> seems to be broken - eg:
>
> $./ssp testtestx
> Illegal instruction
>
> printf's that happen before the stack over-write don't show up & no
> "*** stack smashing detected ***" msg is printed before the "Illegal
> instruction"
> ...
>
> extern
> int doit(char *s ) {
>    char buf[]="12345678";
>    int i=0;
>    if ( *s != '\0' ) i = 1;  /* return true */
>    printf("doit: s=\"%s\"   buf=\"%s\"  i=%d\n", s, buf, i );
>    strcpy(buf, s);
>      /* buffer overflow into return status(int i) if strlen(s) > 8 */
>    printf("doit: s=\"%s\"   buf=\"%s\"  i=%d\n", s, buf, i );
>    return i;
> }
>
> + i686-w64-mingw32-gcc -c -fstack-protector-all func-ssp.c -o func-ssp.o
> + i686-w64-mingw32-gcc -c -fstack-protector-all main-ssp.c -o main-ssp.o
> + i686-w64-mingw32-gcc -static -o ssp.exe func-ssp.o main-ssp.o -lssp

BTW: There is no need to link with -lssp if the related code generation 
option -fstack-protector* is also used during link.


> + ./ssp.exe testtestx
> ./doit: line 11:  9128 Illegal instruction     ./ssp.exe testtestx
> + echo -e '\n\n'
>

The *** stack smashing detected *** message from MinGW runtime is only 
visible if stdio is attached to a Windows console.

Works for me if one more overflow char is added:

Cygwin mintty:

$ ./ssp testtestx
main: argv[1]=testtestx
doit: s="testtestx"   buf="12345678"  i=1
doit: s="testtestx"   buf="testtestx"  i=1
main: exit

$ ./ssp testtestxx
Illegal instruction


Cygwin in Windows console (cygwin.bat):

$ ./ssp testtestxx
main: argv[1]=testtestxx
doit: s="testtestxx"   buf="12345678"  i=1
doit: s="testtestxx"   buf="testtestxx"  i=1
*** stack smashing detected ***:  terminated
Illegal instruction


cmd.exe in Windows console:

C:\cygwin\tmp>.\ssp.exe testtestxx
main: argv[1]=testtestxx
doit: s="testtestxx"   buf="12345678"  i=1
doit: s="testtestxx"   buf="testtestxx"  i=1
*** stack smashing detected ***:  terminated
[Windows Message Box: Debug/Abort Program ?]


Christian


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