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From: Andrew Schulman <andrex AT alumni DOT utexas DOT net>
Subject:  Re: autossh crash with 20050314 and earlier cygwin1.dll [autossh maintainer please note]
Date:  Wed, 16 Mar 2005 12:43:42 -0500
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References:  <20050316162949 DOT GA14571 AT trixie DOT casa DOT cgf DOT cx>
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> The problem is that autossh is freeing the return value of
> gethostbyname().  I can't find any reference which says that is a
> acceptable thing to do.  It certainly screws up cygwin, and I can't
> think of any way to avoid having it screw up cygwin.  Maybe it won't
> screw up other systems since they may not malloc the return value of
> gethostbyname.  I dunno.

OK. (hangs head) I have to take the blame for this, because as it 
happens I contributed that bit of code.  Forgive my simplicity on this 
point, but it seemed like good memory heigene-- free up the memory that 
gethostbyname() allocated, once I was done with it.  Looking back now at 
the man page for gethostbyname() (in Linux, there's no Cygwin man page 
AFAIK), it seems unclear on this point:  the NOTES section says "The 
functions gethostbyname() and gethostbyaddr() *may* return pointers to 
static data, which may be overwritten by later calls." (emphasis added)

This may have been a dumb mistake, or not.  Obviously if the memory is 
static, I shouldn't free() it, but the docs are unclear about whether it 
is or not.  Should I infer that I should not free() memory allocated by 
a function that I call unless the man page specifically says to?  Or 
just that it's best not to free() it if it might be static?  This seems 
like a complicated issue and any pointers for this journeyman network 
programmer would be welcome.  Probably OT for this list, though.

> I haven't run an exhaustive test, but the patch below seems to fix this
> problem.

Confirmed, it fixes my crash here with cygwin1.dll snapshot of 2005-Mar-
11.
 
> Could the autossh maintainer look into getting this applied upstream?

Done.  I'll release a new version shortly.
Andrew.


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