From 323751a604e7533fa473874d999371592a614207 Mon Sep 17 00:00:00 2001 From: Dennis Tighe Date: Tue, 25 Aug 2026 22:09:34 -0700 Subject: [PATCH] ntfs: reject invalid sectors_per_cluster in the boot sector is_boot_sector_ntfs() checks the boot sector's sectors_per_cluster field with a range test that rejects 0x81..0xf3 but accepts 0 and other non-power-of-two counts. A zero value reaches parse_ntfs_boot_sector(): sectors_per_cluster_bits = ffs(sectors_per_cluster) - 1; ... vol->cluster_size = vol->sector_size << sectors_per_cluster_bits; ffs(0) is 0, so sectors_per_cluster_bits becomes (unsigned)-1 and the shift is undefined: UBSAN: shift-out-of-bounds in fs/ntfs/super.c:673:39 shift exponent 4294967295 is too large for 32-bit type 'int' This change rejects any non-power-of-two value, since it feeds the aforementioned shift via ffs() - 1, which only yields the correct shift for a power of two. Fixes: 6251f0b0de7d ("ntfs: update super block operations") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Dennis Tighe Signed-off-by: Namjae Jeon --- fs/ntfs/super.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c index 155dca5db7a9..60d43339c590 100644 --- a/fs/ntfs/super.c +++ b/fs/ntfs/super.c @@ -557,8 +557,8 @@ static bool is_boot_sector_ntfs(const struct super_block *sb, * Check sectors per cluster value is valid and the cluster size * is not above the maximum (2MB). */ - if (b->bpb.sectors_per_cluster > 0x80 && - b->bpb.sectors_per_cluster < 0xf4) + if (b->bpb.sectors_per_cluster < 0xf4 && + !is_power_of_2(b->bpb.sectors_per_cluster)) goto not_ntfs; /* Check reserved/unused fields are really zero. */