child (xterm) fork failure as it loads to different address

[Ryan Johnson]

http://cygwin.com/acronyms/#TOFU

On 29/07/2013 8:15 AM, Ariel Burbaickij wrote:
> OK, thank, you, so usual suspects. Now, removing, antivirus and stuff
> will not be possible in this particular environment but adjustments in
> the configuration are well possible, provided I will be able to prove
> to administrators that troubles, indeed, stem from antivirus and co.
> Now, I see in the FAQ in 4.42 section that these troubles were traced
> and attributed to antiviri programs. Any more details about how they
> were traced exactly, so that I can re-trace them too and provide a
> proof, if needed?
The proof usually goes something like this:

1. People report fork() failures on the list, and a correlation is noted 
between those failures and presence of app/antivirus X.
2. It is confirmed (or at least considered highly probable) that X 
performs dll injection, the root cause of these sorts of fork() failures.
3. Somebody tries disabling/removing X and the fork() failures go away.
4. X gets added to BLODA and reports of fork() failures, not 
attributable to X, disappear from the list.

Eventually the process repeats when Y appears.

You could also try enabling BLODA detection [1] and see what turns up, 
or run the NirSoft DLL injection detector [2].

[1] http://cygwin.com/ml/cygwin/2012-02/msg00797.html
[2] http://www.nirsoft.net/utils/injected_dll.html

> Now, this is for one thing. Another one, is the
> possibility to run Windows 7 (in my case) or any Windows  OS, down to
> and including NT in POSIX-compatible "mode".
 From www.cygwin.com:
> The Cygwin DLL currently works with all recent, commercially released 
> x86 32 bit and 64 bit versions of Windows, starting with Windows XP SP3.
So no, Windows NT will not work. Neither will Win95/98/2000. Nor will XP 
SP1/SP2. But if your admins are really so worried about viruses, they 
won't let you run those ancient operating systems anyway, because MS no 
longer pushes security patches for them.

Given that you seem to have your choice of OS, though, you might try 
64-bit cygwin. The sheer amount of address space that becomes available, 
plus some careful design decisions for placement of cygwin-related dlls 
in that space, reduces the risk of fork failures considerably.

I don't think anybody has reported a fork failure on cygwin64 yet (knock 
on wood). I recently migrated to 64-bit cygwin with a new Win7/64 
install myself, and so far have not had to disable Windows Defender; the 
latter was a recurring source of trouble for my previous 32-bit cygwin 
install on Win7/64.

If you can't get cygwin64 running, you may be able to convince your 
admins to whitelist cygwin apps with the AV solution; that has a small 
chance of stopping the dll injection and allowing fork() to succeed. 
Don't get your hopes up, though: most AV leave the dll injection in 
place even when completely disabled system-wide, and just tell the dlls 
not to do anything (other than stepping on cygwin's toes, of course).

> Is this step expected to
> solve or at least alleviate all or at least some the troubles about
> the square peg of fork() into the round whole of Windows?
cygwin64 may do that... downgrading your OS will not.

Ryan


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