Re: [PATCH 5.8 05/85] Revert "usbip: Implement a match function to fix usbip"

[M. Vefa Bicakci]

On 08/10/2020 05.25, Greg Kroah-Hartman wrote:
> On Thu, Oct 08, 2020 at 04:56:56AM -0400, M. Vefa Bicakci wrote:
> > On 07/10/2020 12.13, Greg Kroah-Hartman wrote:
> > > On Tue, Oct 06, 2020 at 04:26:27PM +0300, M. Vefa Bicakci wrote:
> > > > On 05/10/2020 18.26, Greg Kroah-Hartman wrote:
> > > > > From: M. Vefa Bicakci <m.v.b@xxxxxxxxxx>
> > > > >
> > > > > commit d6407613c1e2ef90213dee388aa16b6e1bd08cbc upstream.
> > > > >
> > > > > This commit reverts commit 7a2f2974f265 ("usbip: Implement a match
> > > > > function to fix usbip").
> > > > >
> > > > > In summary, commit d5643d2249b2 ("USB: Fix device driver race")
> > > > > inadvertently broke usbip functionality, which I resolved in an incorrect
> > > > > manner by introducing a match function to usbip, usbip_match(), that
> > > > > unconditionally returns true.
> > > > >
> > > > > However, the usbip_match function, as is, causes usbip to take over
> > > > > virtual devices used by syzkaller for USB fuzzing, which is a regression
> > > > > reported by Andrey Konovalov.
> > > > >
> > > > > Furthermore, in conjunction with the fix of another bug, handled by another
> > > > > patch titled "usbcore/driver: Fix specific driver selection" in this patch
> > > > > set, the usbip_match function causes unexpected USB subsystem behaviour
> > > > > when the usbip_host driver is loaded. The unexpected behaviour can be
> > > > > qualified as follows:
> > > > > - If commit 41160802ab8e ("USB: Simplify USB ID table match") is included
> > > > >      in the kernel, then all USB devices are bound to the usbip_host
> > > > >      driver, which appears to the user as if all USB devices were
> > > > >      disconnected.
> > > > > - If the same commit (41160802ab8e) is not in the kernel (as is the case
> > > > >      with v5.8.10) then all USB devices are re-probed and re-bound to their
> > > > >      original device drivers, which appears to the user as a disconnection
> > > > >      and re-connection of USB devices.
> > > > >
> > > > > Please note that this commit will make usbip non-operational again,
> > > > > until yet another patch in this patch set is merged, titled
> > > > > "usbcore/driver: Accommodate usbip".
> > > > >
> > > > > Cc: <stable@xxxxxxxxxxxxxxx> # 5.8: 41160802ab8e: USB: Simplify USB ID table match
> > > > > Cc: <stable@xxxxxxxxxxxxxxx> # 5.8
> > > >
> > > > Hello Greg,
> > > >
> > > > Sorry for the lateness of this e-mail.
> > > >
> > > > I had noted commit 41160802ab8e ("USB: Simplify USB ID table match") as a
> > > > prerequisite in the commit message, but I just realized that the commit
> > > > identifier refers to a commit in my local git tree, and not to the actual
> > > > commit in Linus Torvalds' git tree! I apologize for this mistake.
> > > >
> > > > Here is the correct commit identifier:
> > > >     0ed9498f9ecfde50c93f3f3dd64b4cd5414d9944 ("USB: Simplify USB ID table match")
> > > >
> > > > Perhaps this is why the prerequisite commit was not cherry-picked to the 5.8.y
> > > > branch.
> > > >
> > > > As a justification for the cherry-pick, commit 0ed9498f9ecf actually resolves
> > > > a bug. In summary, this commit works together with commit adb6e6ac20ee ("USB:
> > > > Also match device drivers using the ->match vfunc", which has been cherry-picked
> > > > as part of v5.8.6) and ensures that a USB driver's ->match function is also
> > > > called during the search for a more specialized/appropriate USB driver, in case
> > > > the driver in question does not have an id_table.
> > > >
> > > > If I am to be the devil's advocate, however, then given that there is only one
> > > > specialized USB device driver ("apple-mfi-fastcharge"), which conveniently has
> > > > an id_table, and also given that usbip no longer has a match function, I also
> > > > realize that it may not be crucial to cherry-pick 0ed9498f9ecf as a prerequisite
> > > > commit.
> > >
> > > I'm sorry, but I don't really understand.  Does 5.8.y need an additional
> > > patch here, or is all ok because I missed the above patch?
> >
> > No worries; sorry for not communicating clearly and for the delay.
> >
> > I meant to state that it would be good to have commit 0ed9498f9ecf ("USB: Simplify
> > USB ID table match") cherry picked to 5.8.y, as it fixes a bug, albeit a minor one.
>
> What bug does it fix now?  Is usbip or the apple charger driver not
> working properly on 5.8.14?  If nothing is broken, no need to add this
> patch...

I had tried to describe the bug in my original e-mail; it involves not considering
the match functions of candidate USB drivers when determining whether a more
specialized driver exists for a USB device. The bug takes effect when a candidate
USB driver does not have an id_table, but has a match function.

To the best of my current understanding, however, the impact of the bug is
currently none/negligible, because the only specialized driver is currently
the Apple charger driver, and the Apple charger driver uses an id_table and
not a match function.

All this to say, given your last statement, and having thought about the whole
thing one more time, perhaps we do not need to cherry-pick the aforementioned
commit. Sorry for the noise!

Thank you,

Vefa