From: Michael Bommarito Date: Thu, 18 Jun 2026 14:39:22 +0000 (-0400) Subject: minix: avoid overflow in bitmap block count calculation X-Git-Tag: v7.2-rc2~14^2~14 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=fb3e566cafc38fe3ba35e6843a2d529a3748870c;p=thirdparty%2Flinux.git 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. Fixes: 8c97a6ddc956 ("minix: Add required sanity checking to minix_check_superblock()") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Link: https://patch.msgid.link/20260618143922.3066874-1-michael.bommarito@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) --- diff --git a/fs/minix/minix.h b/fs/minix/minix.h index f2025c9b5825..9e52d4302f0d 100644 --- a/fs/minix/minix.h +++ b/fs/minix/minix.h @@ -97,7 +97,7 @@ static inline struct minix_inode_info *minix_i(struct inode *inode) static inline unsigned minix_blocks_needed(unsigned bits, unsigned blocksize) { - return DIV_ROUND_UP(bits, blocksize * 8); + return DIV_ROUND_UP_POW2(bits, blocksize * 8); } #if defined(CONFIG_MINIX_FS_NATIVE_ENDIAN) && \