On Fri, 2 Oct 2026 at 11:22, Thomas Huth <[email protected]> wrote: > > On 01/10/2026 21.47, Peter Maydell wrote: > > The OHCI USB controller requires software to set up an Endpoint > > Descriptor data structure. This specifies (among other things) both > > an EndpointNumber telling the controller which USB endpoint to talk > > to, and a Format (F) bit which is 1 for Isochronous transfers and 0 > > for General transfers. > > > > The specification requires that software matches the F bit with the > > endpoint it's setting up the descriptor for, so that Control, Bulk > > and Interrupt endpoints use F=0, and Isochronous endpoints use F=1. > > It doesn't require the controller to check whether software gets this > > right. > > > > The spec isn't totally clear about what happens if software creates > > an ED with a mismatch, but I believe that the controller just trusts > > the F bit, and tries to talk to the endpoint with the wrong sequence > > of USB tokens (notably, isochronous transactions have no handshaking > > and the others do). This probably results in the transfer failing. > > > > In hcd-ehci.c we check for the "iso transfer to non-iso endpoint" and > > make it fail, but we don't do this in hcd-ohci.c. The result is that > > a guest that deliberately sets up this situation can cause us to hit > > the assertion added in commit 7b1eba96aeca, where the endpoint is not > > isochronous and returns USB_RET_ASYNC to an iso TD handling function > > that isn't prepared to deal with that. > > > > Add checks for both "iso transfer to non-iso endpoint" and "non-iso > > transfer to iso endpoint" and make those TDs fail rather than blindly > > sending them to the endpoint. > > > > Cc: [email protected] > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3729 > Looks like this issue got assigned with a CVE number, so please add: > > CVE: CVE-2026-7180
I guess we might as well, but honestly I don't think this is CVE worthy, and I can't find any record of what that CVE number is supposed to cover from a websearch. This is in OHCI, which I thought was agreed to be outside the security envelope, and in any case it's only an assertion failure. The use-after-free that was the original subject of the bug report has already been fixed by 7b1eba96aeca (which downgraded it to "fails assertion"). thanks -- PMM
