stack overflow bug in ofstream::operator<<

Dave Korn
Tue Jun 28 16:06:00 GMT 2005

----Original Message----
>From: Corinna Vinschen
>Sent: 28 June 2005 16:57

> I had something like that as a local patch but that's a bit dangerous.

  Well, yeh.  But somewhat less dangerous than the existing situation!

> Imagine a process using lots of stack space before calling writev and
> there's only, say, 32K left.  

  Imagine a process using no stack space at all before calling writev and
there's only, say, 2Mb left.  Oh, hang on, that's where we came in!

> It would potentially get a SEGV since
> alloca is used while it would still work when using malloc.  Of course
> malloc could fail for a process using lots of malloc'ed space.  However,
> malloc should at least not SEGV but just return with a NULL pointer...

  Indeed, and perhaps the best fix of all would be if alloca was able to
return NULL when there wasn't enough space on the stack.

> So, I guess I'll just check it in using malloc.

  Hmm.  Can't we tell how much space there is on the stack from the pointers
to the stack limits in the NT_TIB (or whatever lives at %fs on 9x), where we
get the tls pointers from?

Can't think of a witty .sigline today....

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