points by markasoftware 1 day ago | 0 comments
This is not a new vulnerability, it's just a description of how to exploit the PwnEscape vulnerability in practice on firecracker VMs (disclosed multiple weeks ago and discussed in some less upvoted posts on HN)
[–] YetAnotherNick 1 day ago
[–] tptacek 1 day ago
The actual vulnerability got very little discussion. It's clever. Because Linux networking people are obsessed with checksum performance, virtio-net plumbs checksum offload metadata through the host/guest driver interface. Guests can thus deliver the host packets along with instructions on what to checksum. The vulnerability is a missing sanity check that allows checksum instructions to instruct the host to overwrite the header length field in the IPv4 header, rather than the checksum field.
Crucially, this happens in the middle of packet processing, so the kernel code is forced to work with two different ideas of how long the IPv4 header is. All hell predictably breaks loose.
[–] catlifeonmars 1 day ago
That’s fascinating. I’ve seen this sort of thing on protocol implementations in layer 4+ but it’s rare to find it in layer 3.
[–] ytxm 1 day ago
Fixed a month ago upstream
https://github.com/torvalds/linux/commit/6785011f8b16abf40b1...
[–] sscaryterry 15 hours ago
And honestly, how the &*DK is this ANYTHING related to firecracker?
[–] markasoftware 1 day ago
Ah maybe not on HN, I forget where I learned of it. Either way, multiple weeks ago: https://news.ycombinator.com/item?id=50108845
Couldn't find it. Care to provide link.