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Message-ID: <20110921135053.GA12347@openwall.com>
Date: Wed, 21 Sep 2011 17:50:53 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: 1.7.8-jumbo-6-RC* on Mac OS X
Jim -
On Wed, Sep 21, 2011 at 05:25:12PM +0400, Solar Designer wrote:
> Your md5_gen code is complicated, so I think I'll leave further
> investigation to you. What I found out is that Setup->pConstants is
> sometimes NULL and sometimes a non-NULL invalid pointer.
After some playing with gcc options, I am now getting Setup->pFuncs of
NULL, so md5_gen_SETUP() crashes sooner. %-)
It is an uninitialized value if we trust gdb's hardware-assisted
watchpoints. I set two of them: on write and on read. Only the read
one was triggered, on the NULL read right before the place where
md5_gen_SETUP() crashes.
(gdb) watch *0xc3004
Hardware watchpoint 1: *798724
(gdb) rwatch *0xc3004
Hardware read watchpoint 2: *798724
(gdb) r
Starting program: /Users/user/john/john-1.7.8-jumbo-6-RC6/run/john
Reading symbols for shared libraries +++++. done
Hardware watchpoint 1: *798724
Hardware read watchpoint 2: *798724
md5_gen_SETUP: 0xc3000
md5_gen_SETUP: 0xc3000
Hardware read watchpoint 2: *798724
Value = 0
0x0001f3f2 in md5_gen_SETUP ()
(gdb) disass $pc-20 $pc+20
Dump of assembler code from 0x1f3de to 0x1f406:
0x0001f3de <md5_gen_SETUP+94>: mov -0x5c(%ebp),%eax
0x0001f3e1 <md5_gen_SETUP+97>: mov %eax,0x4(%esp)
0x0001f3e5 <md5_gen_SETUP+101>: mov (%edi),%eax
0x0001f3e7 <md5_gen_SETUP+103>: mov %eax,(%esp)
0x0001f3ea <md5_gen_SETUP+106>: call 0x1f5485 <dyld_stub_fprintf>
0x0001f3ef <md5_gen_SETUP+111>: mov 0x4(%esi),%eax
0x0001f3f2 <md5_gen_SETUP+114>: lea -0x5b(%ebx),%edx
0x0001f3f8 <md5_gen_SETUP+120>: mov %edx,-0x54(%ebp)
0x0001f3fb <md5_gen_SETUP+123>: cmp %edx,(%eax)
0x0001f3fd <md5_gen_SETUP+125>: je 0x205d2 <md5_gen_SETUP+4690>
0x0001f403 <md5_gen_SETUP+131>: lea -0x4b(%ebx),%ecx
End of assembler dump.
%esi is Setup, 0x4(%esi) is &Setup->pFuncs
Alexander
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