On Mon, Apr 25, 2022 at 4:41 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > On Sat, 23 Apr 2022 18:07:23 +0200 Lukas Wunner wrote: > > > Looking at the original report it looks like the issue could be > > > resolved with a more usb-specific change: e.g. it looks like > > > usbnet_defer_kevent() is not acquiring a dev reference as it should. > > > > > > Have you considered that path? > > > > First of all, the diffstat of the patch shows this is an opportunity > > to reduce LoC as well as simplify and speed up device teardown. > > > > Second, the approach you're proposing won't work if a driver calls > > netif_carrier_on/off() after unregister_netdev(). > > > > It seems prudent to prevent such a misbehavior in *any* driver, > > not just usbnet. usbnet may not be the only one doing it wrong. > > Jann pointed out that there are more syzbot reports related > > to a UAF in linkwatch: > > > > https://lore.kernel.org/netdev/?q=__linkwatch_run_queue+syzbot > > > > Third, I think an API which schedules work, invisibly to the driver, > > is dangerous and misguided. If it is illegal to call > > netif_carrier_on/off() for an unregistered but not yet freed netdev, > > catch that in core networking code and don't expect drivers to respect > > a rule which isn't even documented. > > Doesn't mean we should make it legal. We can add a warning to catch > abuses. That was the idea with https://lore.kernel.org/netdev/20220128014303.2334568-1-jannh@xxxxxxxxxx/, but I didn't get any replies when I asked what the precise semantics of dev_hold() are supposed to be (https://lore.kernel.org/netdev/CAG48ez1-OyZETvrYAfaHicYW1LbrQUVp=C0EukSWqZrYMej73w@xxxxxxxxxxxxxx/), so I don't know how to proceed...
