ACK/Cmnt: [SRU][F][PATCH 0/1] CVE-2024-26996

[Massimiliano Pellizzer]

On Thu, 20 Mar 2025 at 15:19, Kuba Pawlak <kuba.pawlak at canonical.com> wrote:
>
> On 18.03.2025 17:59, Edoardo Canepa wrote:
>
> > https://ubuntu.com/security/CVE-2024-26996
> >
> > [ Impact ]
> >
> > usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error
> > When ncm function is working and then stop usb0 interface for link down,
> > eth_stop() is called. At this piont, accidentally if usb transport error
> > should happen in usb_ep_enable(), 'in_ep' and/or 'out_ep' may not be enabled.
> >
> > After that, ncm_disable() is called to disable for ncm unbind
> > but gether_disconnect() is never called since 'in_ep' is not enabled.
> >
> > As the result, ncm object is released in ncm unbind
> > but 'dev->port_usb' associated to 'ncm->port' is not NULL.
> >
> > And when ncm bind again to recover netdev, ncm object is reallocated
> > but usb0 interface is already associated to previous released ncm object.
> >
> > Therefore, once usb0 interface is up and eth_start_xmit() is called,
> > released ncm object is dereferrenced and it might cause use-after-free memory.
> >
> > [function unlink via configfs]
> >    usb0: eth_stop dev->port_usb=ffffff9b179c3200
> >    --> error happens in usb_ep_enable().
> >    NCM: ncm_disable: ncm=ffffff9b179c3200
> >    --> no gether_disconnect() since ncm->port.in_ep->enabled is false.
> >    NCM: ncm_unbind: ncm unbind ncm=ffffff9b179c3200
> >    NCM: ncm_free: ncm free ncm=ffffff9b179c3200   <-- released ncm
> >
> > [function link via configfs]
> >    NCM: ncm_alloc: ncm alloc ncm=ffffff9ac4f8a000
> >    NCM: ncm_bind: ncm bind ncm=ffffff9ac4f8a000
> >    NCM: ncm_set_alt: ncm=ffffff9ac4f8a000 alt=0
> >    usb0: eth_open dev->port_usb=ffffff9b179c3200  <-- previous released ncm
> >    usb0: eth_start dev->port_usb=ffffff9b179c3200 <--
> >    eth_start_xmit()
> >    --> dev->wrap()
> >    Unable to handle kernel paging request at virtual address dead00000000014f
> >
> > This patch addresses the issue by checking if 'ncm->netdev' is not NULL at
> > ncm_disable() to call gether_disconnect() to deassociate 'dev->port_usb'.
> > It's more reasonable to check 'ncm->netdev' to call gether_connect/disconnect
> > rather than check 'ncm->port.in_ep->enabled' since it might not be enabled
> > but the gether connection might be established.
> >
> > [ Fix ]
> >
> > Oracular:       not affected
> > Noble:          fixed via stable updates
> > Jammy:          fixed via stable updates
> > Focal:          backport
> > Bionic:         backport
> > Xenial:         backport
> > trusty:         won't fix
> >
> > [ Test Plan ]
> >
> > * Build test for all supported architectures.
> > * Boot tested on amd64 architecture.
> >
> > [ Where Problems Could Occur ]
> >
> > This changes the handling of object re-bind after USB ep error, so it is unlikely
> > that impacts anything beyond this use case. An issue with this fix would be
> > visible with usb connect/disconnect cycle.
> >
> > [ Other Info ]
> >
> > N/A
> >
> >
> Acked-by: Kuba Pawlak <kuba.pawlak at canonical.com>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

Please remember next time to add v2 in the subject
and specify in the cover letter what changed between v1 and v2.

Other than that the patch looks good to me.
Smatch tested.

Acked-by: Massimiliano Pellizzer <massimiliano.pellizzer at canonical.com>

-- 
Massimiliano Pellizzer