Re: [PATCH] Input: try trimming too long modalias strings

Greg KH
2024-06-12T12:17:10Z

On Mon, May 27, 2024 at 03:55:57PM -0400, Jason Andryuk wrote:
> From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
>
> commit 0774d19038c496f0c3602fb505c43e1b2d8eed85 upstream.
>
> If an input device declares too many capability bits then modalias
> string for such device may become too long and not fit into uevent
> buffer, resulting in failure of sending said uevent. This, in turn,
> may prevent userspace from recognizing existence of such devices.
>
> This is typically not a concern for real hardware devices as they have
> limited number of keys, but happen with synthetic devices such as
> ones created by xen-kbdfront driver, which creates devices as being
> capable of delivering all possible keys, since it doesn't know what
> keys the backend may produce.
>
> To deal with such devices input core will attempt to trim key data,
> in the hope that the rest of modalias string will fit in the given
> buffer. When trimming key data it will indicate that it is not
> complete by placing "+," sign, resulting in conversions like this:
>
> old: k71,72,73,74,78,7A,7B,7C,7D,8E,9E,A4,AD,E0,E1,E4,F8,174,
> new: k71,72,73,74,78,7A,7B,7C,+,
>
> This should allow existing udev rules continue to work with existing
> devices, and will also allow writing more complex rules that would
> recognize trimmed modalias and check input device characteristics by
> other means (for example by parsing KEY= data in uevent or parsing
> input device sysfs attributes).
>
> Note that the driver core may try adding more uevent environment
> variables once input core is done adding its own, so when forming
> modalias we can not use the entire available buffer, so we reduce
> it by somewhat an arbitrary amount (96 bytes).
>
> Reported-by: Jason Andryuk <jandryuk@gmail.com>
> Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
> Tested-by: Jason Andryuk <jandryuk@gmail.com>
> Link: https://lore.kernel.org/r/ZjAWMQCJdrxZkvkB@google.com
> Cc: stable@vger.kernel.org
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> [ Apply to linux-6.1.y ]
> Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
> ---
> Patch did not automatically apply to 6.1.y because
> input_print_modalias_parts() does not have const on *id.
>
> Tested on 6.1. Seems to also apply and build on 5.4 and 4.19.

How was this tested?

It blows up the build on all branches, 6.1 and older kernels with a ton
of errors like:
drivers/input/input.c: In function ‘input_print_modalias_parts’:
drivers/input/input.c:1397:40: error: passing argument 4 of ‘input_print_modalias_bits’ discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
1397 | 'e', id->evbit, 0, EV_MAX);
| ~~^~~~~~~

And so on.

Are you sure you sent the right patch?

thanks,

greg k-h