CVE-2026-23235

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/carve_out

vm:~# cat /sys/fs/f2fs/vde/carve_out

65537

vm:~# echo 4294967297 > /sys/fs/f2fs/vde/atgc_age_threshold

vm:~# cat /sys/fs/f2fs/vde/atgc_age_threshold

1

carve_out maps to {struct f2fs_sb_info}->carve_out, 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.

atgc_age_threshold maps to {struct atgc_management}->age_threshold,

which is a 64-bit integer, but its sysfs interface cannot correctly set

values larger than UINT_MAX.

The root causes are:

1. __sbi_store() 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. f2fs_sbi_show() 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 f2fs_attr}->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.