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Re: Dangerous use of alloca


From: Samuel Thibault
Subject: Re: Dangerous use of alloca
Date: Tue, 15 Mar 2016 18:30:16 +0100
User-agent: Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30)

Justus Winter, on Tue 15 Mar 2016 18:10:18 +0100, wrote:
> Quoting Samuel Thibault (2016-03-15 17:31:53)
> > Justus Winter, on Tue 15 Mar 2016 14:39:00 +0100, wrote:
> > > Quoting Agustina Arzille (2016-03-15 14:11:27)
> > > > Hello, everyone.
> > > > 
> > > > I was browsing some gnumach source files, and noticed some dangerous use
> > > > of the gcc builtin 'alloca'. In the file kern/bootstrap.c, lines 212 and
> > > > 228, we have the following statement:
> > > > 
> > > > memcpy (alloca (len), ...)
> > > 
> > > Good catch.  However, alloca is dangerous even if used correctly, and
> > > is best be avoided.
> > 
> > What do you mean by "dangerous"?  I don't think we'll ever get a command
> > line that does not fit into the stack.
> 
> I don't see why not actually, unless grub limits this somehow O:-)

It doesn't indeed, so it is definitely possible; I just don't see
anybody typing a 4096-characters command line :)

Samuel



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