[TUHS] The evolution of Unix facilities and architecture

Random832 random832 at fastmail.com
Sat May 13 10:48:35 AEST 2017

On Fri, May 12, 2017, at 20:26, Dave Horsfall wrote:
> On Fri, 12 May 2017, Random832 wrote:
> > > > 	if (xp->x_count!=1 || xp->x_iptr->i_mode&ISVTX)
> > > > 		goto error;
> > > 
> > > Err, isn't that the sticky bit, not the setuid bit?
> > 
> > The sticky bit makes it keep the image in memory when there are no 
> > processes using it. I assume x_count is determining whether there are 
> > processes using it. So, taken together, these checks are "is there or 
> > might there be in the future a process, other than the one being 
> > debugged, using this exact copy of the image rather than loading it from 
> > the disk".
> I know that, but the discussion was about the SUID bit, and the ability
> to 
> modify the in-core image of a set-uid program being run...

It seems to me that this check is central to being able to (or not)
modify the in-core image of any process at all other than the one being
traced (say, by attaching to a SUID program that has already dropped
privileges, and making changes that will affect the next time it is

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