alt Hacker NewsI really wish they would have expanded on this paragraph in their article further:
> The configuration used here had no jailer. Firecracker's production containment includes dropping privileges and restricting the process through namespaces and seccomp. A deployment using those controls requires a separate assessment of the privileges and resources available after compromising its VMM.
If I'm understanding all of this correctly, a properly jailed and configured firecracker instance would greatly reduce the blast radius of this escape, and I feel as though it would have been good for them to explain what jailing and dropping privileges would do to help. I'd hope most production firecracker deployments would be doing this already.
Not saying that this is any less severe and the root issue is not specific to Firecracker, but to a flaw in the kernel's network code -- they just used an insecure firecracker configuration to demonstrate it. However, I feel like some are taking this as a flaw with firecracker when its not. This is an issue in the kernel networking stack.
Replies
> This is an issue in the kernel networking stack.
Exactly, its not a firecracker issue. Using firecracker without a jailer is like setting your password to "password".
Nope. The exploit compromises the host kernel. The researchers built an unconventional exploit chain in which they used the host kernel compromise to compromise the host firecracker userspace code, but I see no fundamental reason they couldn't have compromised something else in the host kernel.
yup, the other firecracker escape recently (https://www.coinspect.com/blog/firecracker-escape/) popped the jailer via io_uring (tl;dr firecracker was filtering syscalls appropriately with seccomp, and was filtering the uring _they_ initiated, so attacker just got them to pop a new unfiltered uring, which is rather nice).
That's a good catch. Yes, since they've only proven this up to the jailer boundary, you'd need a second and relatively powerful LPE vulnerability to get real host control out of this.