CVE-2026-23235: f2fs: fix out-of-bounds access in sysfs attribute read/write

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix out-of-bounds access in sysfs attribute read/write

Some f2fs sysfs attributes suffer from out-of-bounds memory access and incorrect handling of integer values whose size is not 4 bytes.

For example: vm:~# echo 65537 > /sys/fs/f2fs/vde/carveout vm:~# cat /sys/fs/f2fs/vde/carveout 65537 vm:~# echo 4294967297 > /sys/fs/f2fs/vde/atgcagethreshold vm:~# cat /sys/fs/f2fs/vde/atgcagethreshold 1

carveout maps to {struct f2fssbinfo}->carveout, which is a 8-bit integer. However, the sysfs interface allows setting it to a value larger than 255, resulting in an out-of-range update.

atgcagethreshold maps to {struct atgcmanagement}->agethreshold, which is a 64-bit integer, but its sysfs interface cannot correctly set values larger than UINTMAX.

The root causes are: 1. sbistore() treats all default values as unsigned int, which prevents updating integers larger than 4 bytes and causes out-of-bounds writes for integers smaller than 4 bytes.

2. f2fssbishow() also assumes all default values are unsigned int, leading to out-of-bounds reads and incorrect access to integers larger than 4 bytes.

This patch introduces {struct f2fsattr}->size to record the actual size of the integer associated with each sysfs attribute. With this information, sysfs read and write operations can correctly access and update values according to their real data size, avoiding memory corruption and truncation.