linux-kernel - [PATCH] Input: xen-kbdfront - drop keys to shrink modalias

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Date:   Wed, 19 Oct 2022 16:14:57 -0400
From:   Jason Andryuk <jandryuk@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org, Jason Andryuk <jandryuk@...il.com>,
        Phillip Susi <phill@...susis.net>, stable@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input@...r.kernel.org
Subject: [PATCH] Input: xen-kbdfront - drop keys to shrink modalias

xen kbdfront registers itself as being able to deliver *any* key since
it doesn't know what keys the backend may produce.

Unfortunately, the generated modalias gets too large and uevent creation
fails with -ENOMEM.

This can lead to gdm not using the keyboard since there is no seat
associated [1] and the debian installer crashing [2].

Trim the ranges of key capabilities by removing some BTN_* ranges.
While doing this, some neighboring undefined ranges are removed to trim
it further.

This removes:
BTN_DPAD_UP(0x220)..BTN_DPAD_RIGHT(0x223)
Empty space 0x224..0x229

Emtpy space 0x2bd..0x2bf
BTN_TRIGGER_HAPPY(0x2c0)..BTN_TRIGGER_HAPPY40(0x2e7)
Empty space 0x2e8..0x2ff

The modalias shrinks from 2082 to 1754 bytes.

[1] https://github.com/systemd/systemd/issues/22944
[2] https://lore.kernel.org/xen-devel/87o8dw52jc.fsf@vps.thesusis.net/T/

Cc: Phillip Susi <phill@...susis.net>
Cc: stable@...r.kernel.org
Signed-off-by: Jason Andryuk <jandryuk@...il.com>
---
 drivers/input/misc/xen-kbdfront.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/input/misc/xen-kbdfront.c b/drivers/input/misc/xen-kbdfront.c
index 8d8ebdc2039b..23f37211be78 100644
--- a/drivers/input/misc/xen-kbdfront.c
+++ b/drivers/input/misc/xen-kbdfront.c
@@ -256,7 +256,14 @@ static int xenkbd_probe(struct xenbus_device *dev,
 		__set_bit(EV_KEY, kbd->evbit);
 		for (i = KEY_ESC; i < KEY_UNKNOWN; i++)
 			__set_bit(i, kbd->keybit);
-		for (i = KEY_OK; i < KEY_MAX; i++)
+		/* In theory we want to go KEY_OK..KEY_MAX, but that grows the
+		 * modalias line too long.  KEY_KBD_LCD_MENU5 is the last
+		 * defined non-button key. There is a gap of buttons from
+		 * BTN_DPAD_UP..BTN_DPAD_RIGHT and KEY_ALS_TOGGLE is the next
+		 * defined. */
+		for (i = KEY_OK; i < BTN_DPAD_UP; i++)
+			__set_bit(i, kbd->keybit);
+		for (i = KEY_ALS_TOGGLE; i <= KEY_KBD_LCD_MENU5; i++)
 			__set_bit(i, kbd->keybit);
 
 		ret = input_register_device(kbd);
-- 
2.37.3