usbnet: ipheth: fix connectivity with iOS 14

Starting with iOS 14 released in September 2020, connectivity using the
personal hotspot USB tethering function of iOS devices is broken.

Communication between the host and the device (for example ICMP traffic
or DNS resolution using the DNS service running in the device itself)
works fine, but communication to endpoints further away doesn't work.

Investigation on the matter shows that UDP and ICMP traffic from the
tethered host is reaching the Internet at all. For TCP traffic there are
exchanges between tethered host and server but packets are modified in
transit leading to impossible communication.

After some trials Matti Vuorela discovered that reducing the URB buffer
size by two bytes restored the previous behavior. While a better
solution might exist to fix the issue, since the protocol is not
publicly documented and considering the small size of the fix, let's do
that.

Tested-by: Matti Vuorela <matti.vuorela@bitfactor.fi>
Signed-off-by: Yves-Alexis Perez <corsac@corsac.net>
Link: https://lore.kernel.org/linux-usb/CAAn0qaXmysJ9vx3ZEMkViv_B19ju-_ExN8Yn_uSefxpjS6g4Lw@mail.gmail.com/
Link: https://github.com/libimobiledevice/libimobiledevice/issues/1038
Cc: stable@vger.kernel.org
---
 drivers/net/usb/ipheth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hello!

On 19.11.2020 20:24, Yves-Alexis Perez wrote:

> Starting with iOS 14 released in September 2020, connectivity using the
> personal hotspot USB tethering function of iOS devices is broken.
> 
> Communication between the host and the device (for example ICMP traffic
> or DNS resolution using the DNS service running in the device itself)
> works fine, but communication to endpoints further away doesn't work.
> 
> Investigation on the matter shows that UDP and ICMP traffic from the
                                         ^ "no" missing?

> tethered host is reaching the Internet at all. For TCP traffic there are
> exchanges between tethered host and server but packets are modified in
> transit leading to impossible communication.
> 
> After some trials Matti Vuorela discovered that reducing the URB buffer
> size by two bytes restored the previous behavior. While a better
> solution might exist to fix the issue, since the protocol is not
> publicly documented and considering the small size of the fix, let's do
> that.
> 
> Tested-by: Matti Vuorela <matti.vuorela@bitfactor.fi>
> Signed-off-by: Yves-Alexis Perez <corsac@corsac.net>
> Link: https://lore.kernel.org/linux-usb/CAAn0qaXmysJ9vx3ZEMkViv_B19ju-_ExN8Yn_uSefxpjS6g4Lw@mail.gmail.com/
> Link: https://github.com/libimobiledevice/libimobiledevice/issues/1038
> Cc: stable@vger.kernel.org
[...]

MBR, Sergei

On Thu, 19 Nov 2020 18:24:39 +0100 Yves-Alexis Perez wrote:
> Starting with iOS 14 released in September 2020, connectivity using the

> personal hotspot USB tethering function of iOS devices is broken.

> 

> Communication between the host and the device (for example ICMP traffic

> or DNS resolution using the DNS service running in the device itself)

> works fine, but communication to endpoints further away doesn't work.

> 

> Investigation on the matter shows that UDP and ICMP traffic from the

> tethered host is reaching the Internet at all. For TCP traffic there are

> exchanges between tethered host and server but packets are modified in

> transit leading to impossible communication.

> 

> After some trials Matti Vuorela discovered that reducing the URB buffer

> size by two bytes restored the previous behavior. While a better

> solution might exist to fix the issue, since the protocol is not

> publicly documented and considering the small size of the fix, let's do

> that.

> 

> Tested-by: Matti Vuorela <matti.vuorela@bitfactor.fi>

> Signed-off-by: Yves-Alexis Perez <corsac@corsac.net>

> Link: https://lore.kernel.org/linux-usb/CAAn0qaXmysJ9vx3ZEMkViv_B19ju-_ExN8Yn_uSefxpjS6g4Lw@mail.gmail.com/

> Link: https://github.com/libimobiledevice/libimobiledevice/issues/1038


Applied to net with the typo fixed, thanks!

On Sat, 2020-11-21 at 14:03 -0800, Jakub Kicinski wrote:
> Applied to net with the typo fixed, thanks!

Thanks!

Is there any chance it'll be in 5.10 or will it have to wait for the 5.11
merge window?

Also it should be applied to all supported/stable kernels. I guess that'll
have to wait until it's in Linus tree according [1] to but I'm unsure if I
need to trigger the action myself or if Greg (or Dave, according to [2]) will
do it.

I looked at [3] and it seems that adding the CC: stable in my commit message
maybe was an error because it's marked as a Failure, so if there's anything
needed from me here, don't hesitate to ask.

[1] https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
[2]
https://www.kernel.org/doc/html/latest/networking/netdev-FAQ.html#q-how-can-i-tell-what-patches-are-queued-up-for-backporting-to-the-various-stable-releases
[3] https://patchwork.kernel.org/bundle/netdev/stable/?state=*

Regards,

On Tue, 24 Nov 2020 11:41:40 +0100 Yves-Alexis Perez wrote:
> On Sat, 2020-11-21 at 14:03 -0800, Jakub Kicinski wrote:
> > Applied to net with the typo fixed, thanks!  
> 
> Thanks!
> 
> Is there any chance it'll be in 5.10 or will it have to wait for the 5.11
> merge window?

It'll be in 5.10-rc6.

> Also it should be applied to all supported/stable kernels. I guess that'll
> have to wait until it's in Linus tree according [1] to but I'm unsure if I
> need to trigger the action myself or if Greg (or Dave, according to [2]) will
> do it.

Dave (or someone helping him, like myself) will do it, probably around
the time 5.10-rc6 is released.

> I looked at [3] and it seems that adding the CC: stable in my commit message
> maybe was an error because it's marked as a Failure, so if there's anything
> needed from me here, don't hesitate to ask.

No worries, I stripped the CC and put the patch in Dave's stable queue.