lkml.org 
[lkml]   [2007]   [Jun]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Syslets, signals, and security
On Mon, Jun 04, 2007 at 10:45:42AM -0700, Zach Brown wrote:
> > Second, security. What happens if a well-written server starts life
> > as root, does some (async) I/O, and setuids to a non-root uid? There
> > will be a bunch of async threads still running as root, with the
> > result that async operations (and the main thread) will more than
> > occassionally regain root privs.

> One can imagine all sorts of crazy schemes which let us only shoot down
> waiting async threads which were cloned before state in the submitting
> task_struct was changed. Maybe we could swallow increasing a counter in
> task_struct each time we change one of these sensitive fields (fsuid,
> etc), but I bet the maintenance burden of anything more fine grained
> than that would get pretty excessive.

How about splitting the credentials out of the task_struct and making
them sharable ala ->mm et al? You change uid there and it changes for
everyone. It will make fork slightly more expensive though.

> Yeah, and I'm blissfully ignorant of ptrace. Imagine me skipping
> through a field of daisies with some ptrace wolves hiding in the bushes
> at the edge of the meadow. La la la.

Heh, I'm somewhat less ignorant of ptrace, so I'll see if I can help
out there.

> Each execution context having its own task struct is intentional, very
> much so. Remember, this started with the fibrils patch series which
> indeed shared a single task struct amongst a set of running stacks and
> thread infos, etc. This approach is invasive because it changes the
> sleeping entity in the scheduler from a task struct to some new
> construct which has a many to one mapping to the task struct. It
> touches vast amounts of code. This approach is also risky because it
> introduces concurrent access to the task struct. That's a pretty big
> auditing burden.

Yeah, I realize that, but have no idea how much code that requires
looking at.

> Have you looked at how the fibrils stuff did it? It's a lot more work
> than it seems like it should be, on first glance. You start to modify
> things and every few days you trip across another fundamental kernel
> construct which needs to be modified :/.
>
> http://lwn.net/Articles/219954/

Ah, I somehow missed this. Since you seem to have explored that area
of the solution space already and found it wanting, I agree that it
makes sense to see if syslets can be made to work.

Jeff
--
Work email - jdike at linux dot intel dot com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-04 21:25    [W:0.760 / U:0.128 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site