Re: [PATCH] Fix race condition when exec'ing setuid files

[Jorge Merlino <jorge.merlino@canonical.com>]

On 13/9/22 19:03, Kees Cook wrote:
> I'll want to spend some more time studying this race, but yes, it looks
> like it should get fixed. I'm curious, though, how did you find this
> problem? It seems quite unusual to have a high-load heavily threaded
> process decide to exec.

I just got a response from our customer regarding the situation where 
this race condition occurs:


Our application is a Rust-based CLI tool that acts as a frontend to 
cloud-based testing infrastructure. In one mode of operation it uploads 
a large number of test artifacts to cloud storage, spawns compute 
instances, and then starts a VPN connection to those instances. The 
application creates the VPN connection by executing another setuid-root 
tool as a subprocess. We see that this subprocess sometimes fails to 
setuid. The "high-load heavily threaded" aspect comes from the fact that 
we're using the Tokio runtime. Each upload to cloud storage is a 
separate Tokio task (i.e. "green thread") and these are scheduled onto 
"N" OS-level threads, where N = nproc. In a large run we may upload a 
couple thousand artifacts but limit to 50 concurrent uploads. Once these 
artifact uploads complete, we typically spawn the setuid subprocess 
within 1-2 seconds.

Have you been able to look at this issue?

Thanks
	Jorge