CVE-2026-97926ufs: validate cylinder group metadata before caching it

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/88cccb6beba136b73f0caf80e59457e1b3c0ca1e
• https://git.kernel.org/stable/c/f560a9e33365c460827c735fd86435f9213f1aed
• https://git.kernel.org/stable/c/e4c5cc9688c3e69d07d888853388549ae26c0521
• https://git.kernel.org/stable/c/58c0c414b2b8d099d33da494a354fa836ca6c10b
• https://git.kernel.org/stable/c/5902a95066883cf96fa15b2680694fc5dd0c7d11
• https://git.kernel.org/stable/c/87b12dc360a002eb2d498aa4f01e84347019612d
• https://git.kernel.org/stable/c/abde9eb33106850dfa367ad3965d3588bb8558d5
• https://git.kernel.org/stable/c/c9d263be26806d388129fab8c6904bed197fc6af