[rtmpdump] Null dereference in rtmpsuck

Matt Breedlove breedlove.matt at gmail.com
Mon Oct 27 13:06:53 CET 2014

Hey guys,

I've run into a case that happens while running rtmpsuck where a null
dereference will eventually occur.  I'm running a Windows build currently
but this was present in the Linux build also from the latest version on

00402eab 8b0482          mov     eax,dword ptr [edx+eax*4]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 00402eab (image00400000+0x00002eab)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 00000018
Attempt to read from address 00000018

CONTEXT:  00000000 -- (.cxr 0x0;r)
eax=00000006 ebx=0b835be0 ecx=0dce1298 edx=00000000 esi=0e60fdb8
eip=00402eab esp=0e60fd3c ebp=0e60ff14 iopl=0         nv up ei pl zr na pe
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
00402eab 8b0482          mov     eax,dword ptr [edx+eax*4]

rtmpsuck.c on line 818:

server->rc.m_pauseStamp =

compiles to:

mov ecx, [ebx+8418h]
test ecx, ecx
jz short loc_402EE2 # jz server->f_cur
mov eax, [ebx+4224h] # server->rc.m_mediaChannel => eax (6)
test eax, eax
jz short loc_402EE2 # jz server->rc.m_mediaChannel
mov edx, [ebp+var_1A4]
test edx, edx
jnz short loc_402EE2 # jnz paused
mov edx, [ebx+425Ch] # server->rc.m_channelTimestamp => edx (0)
mov eax, [edx+eax*4] # edx(0)+eax(6)*4 == 0x18
mov [ebx+422Ch], eax
mov eax, [ebp+var_19C]
mov [esp], eax
call _RTMP_ToggleStream
test eax, eax

The following patch seems to at least prevent the process from crashing but
I was hoping to get some input in case this might just be a symptom of
another problem.  I'm not familiar enough with the protocol or codebase.
Any thoughts?


<               if (server->f_cur && server->rc.m_mediaChannel &&
server->rc.m_channelTimestamp && !paused)
>               if (server->f_cur && server->rc.m_mediaChannel && !paused)

Matt Breedlove
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