[TUHS] The evolution of Unix facilities and architecture

Noel Chiappa jnc at mercury.lcs.mit.edu
Sat May 13 09:30:12 AEST 2017


    > From: Clem Cole

    > I said -- profil - I intended to say  ptrace(2)

Is that the one where running an SUID program under the debugger allowed one
to patch the in-core image of said program?

If so, I have a story, and a puzzle, about that.


A couple of us, including Jim Gettys (later of X-windows fame) were on out way
out to dinner one evening (I don't recall when, alas, but I didn't meet him
until '80 or so), and he mentioned this horrible Unix security bug that had
just been found. All he would tell me about it (IIRC) was that it involved
ptrace.

So, over dinner (without the source) I figured out what it had to be:
patching SUID programs. So I asked him if that was what it was, and I don't
recall his exact answer, but I vaguely recall he hemmed and hawed in a way
that let me know I'd worked it out.

So when we got back from dinner, I looked at the source to our system to see
if I was right, and.... it had already been fixed! Here's the code:

	if (xp->x_count!=1 || xp->x_iptr->i_mode&ISVTX)
		goto error;

Now, we'd been running that system since '77 (when I joined CSR), without any
changes to that part of the OS, so I'm pretty sure this fix pre-dates your
story?

So when I saw your email about this, I wondered 'did that bug get fixed at
MIT when some undergrad used it to break in' (I _think_ ca. '77 is when they
switched from an OS called Delphi on the -11/45 used for the undergrad CS
programming course - I _think_ they switched that machine from Delphi to
Unix), or did it come with PWB1? (Like I said, that system was mostly PWB1.)

So I just looked in the PWB1 sources, and... there it is, the _exact_ same
fix. So we must have got it from PWB1.

So now the question is: did the PWB guys find and fix this, and forget to
tell the research guys? Or did they tell them, and the research guys blew
them off? Or what?

	Noel


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