CVE-2026-97926

Summary

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 Software

Weaknesses

References

• 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

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