CVE-2026-72369minix: avoid overflow in bitmap block count calculation

Official description

In the Linux kernel, the following vulnerability has been resolved: minix: avoid overflow in bitmap block count calculation minix_check_superblock() uses minix_blocks_needed() to verify that the on-disk imap and zmap block counts are large enough for the advertised inode and zone counts. The helper currently performs DIV_ROUND_UP() in unsigned int arithmetic. A Minix v3 image can set s_ninodes or s_zones near UINT_MAX so the addition inside DIV_ROUND_UP() wraps to zero. That makes a zero imap/zmap block count look valid, after which minix_fill_super() can dereference s_imap[0] or s_zmap[0] even though no bitmap buffers were allocated. Impact: mounting a crafted Minix v3 image whose s_ninodes or s_zones is near UINT_MAX makes minix_check_superblock() accept a zero bitmap-block count and minix_fill_super() dereference s_imap[0]/s_zmap[0], panicking the kernel. The divisor is the bitmap capacity in bits, blocksize * 8, which is always a power of two: minix_fill_super() obtains the block size through sb_set_blocksize(), and blk_validate_block_size() rejects any size that is not a power of two. Use DIV_ROUND_UP_POW2(), which divides before adding the round-up term and so cannot overflow for a power-of-two divisor.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/a11ebaab50d27d6c4c78506f84ff36452e0b901d
• https://git.kernel.org/stable/c/959c95340a9e19cd333b4c18935fdeecbb2f319d
• https://git.kernel.org/stable/c/abe3536a4bedcc43de80b6d4d7e3d57e9ba382a5
• https://git.kernel.org/stable/c/8a29e60e2176b02e04f8737c8b32b696230eb0c5
• https://git.kernel.org/stable/c/fb3e566cafc38fe3ba35e6843a2d529a3748870c