Input: evdev - zero absinfo before partial copy in EVIOCSABS

The EVIOCSABS handler copies at most the user supplied ioctl size into
an uninitialized on-stack struct input_absinfo:

	if (copy_from_user(&abs, p, min_t(size_t,
			size, sizeof(struct input_absinfo))))

The size comes from _IOC_SIZE() of the ioctl command and is therefore
fully controlled by userspace. A short size leaves the trailing part of
the structure holding whatever was on the kernel stack, and the whole
structure is then stored into the device:

	dev->absinfo[t] = abs;

EVIOCGABS hands that back to userspace, disclosing the stale stack
bytes. Only the resolution field is currently cleared, which covers the
legacy struct layout but not an arbitrarily short size.

Zero the structure before the copy so any part not supplied by the
caller reads back as zero. The existing resolution fixup is kept, since
it also handles a size that partially overlaps that field.

Fixes: 448cd1664a ("Input: evdev - rearrange ioctl handling")
Cc: stable@vger.kernel.org
Signed-off-by: Iván Ezequiel Rodriguez <ivanrwcm25@gmail.com>
Link: https://patch.msgid.link/20260901130629.24078-2-ivanrwcm25@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/evdev.c

@@ -1229,6 +1229,8 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 
 			t = _IOC_NR(cmd) & ABS_MAX;
 
+			memset(&abs, 0, sizeof(abs));
+
 			if (copy_from_user(&abs, p, min_t(size_t,
 					size, sizeof(struct input_absinfo))))
 				return -EFAULT;