CVE-2026-97926

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

ufs: validate cylinder group metadata before caching it

ufs_read_cylinder() copies the cylinder group index and the rotor

positions straight from the on-disk group and caches them without any

check:

ucpi->c_cgx = fs32_to_cpu(sb, ucg->cg_cgx);

ucpi->c_rotor = fs32_to_cpu(sb, ucg->cg_rotor);

ucpi->c_frotor = fs32_to_cpu(sb, ucg->cg_frotor);

ucpi->c_irotor = fs32_to_cpu(sb, ucg->cg_irotor);

They are then used as indices during allocation and free:

- c_cgx indexes the cylinder summary array as

UFS_SB(sb)->fs_cs(ucpi->c_cgx), so a value past s_ncg writes a 32

bit count outside the s_csp allocation.

- c_frotor becomes a bitmap scan start, start = c_frotor >> 3, and

then length = ((s_fpg + 7) >> 3) - start. A start beyond the block

bitmap wraps the unsigned length to a huge value, so ubh_scanc()

walks far past the cylinder group buffers. c_irotor drives the

inode bitmap the same way.

A crafted image can set any of these freely, turning an ordinary

allocation into an out of bounds access.

Reject a cylinder group whose recorded index does not match the group

being read, or whose rotors fall outside the group, before the metadata

is cached. Valid filesystems keep cg_cgx equal to the group number and

the rotors within the group, so only malformed images are rejected.