From: Karel Zak Date: Thu, 30 Oct 2025 11:11:43 +0000 (+0100) Subject: libfdisk: (dos) fix off-by-one in maximum last sector calculation X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=578923fe582903628ecc0d2a434af0affa3660d2;p=thirdparty%2Futil-linux.git libfdisk: (dos) fix off-by-one in maximum last sector calculation The get_disk_ranges() function incorrectly capped the last usable sector at UINT_MAX, which could cause an overflow when calculating partition size for MBR partition tables. MBR stores partition size as a 32-bit value with maximum UINT_MAX. The partition size is calculated as: size = stop - start + 1 For a partition starting at sector 0: - If stop = UINT_MAX: size = UINT_MAX + 1 (overflow!) - If stop = UINT_MAX - 1: size = UINT_MAX (correct maximum) This fixes the inconsistency where dos_init() correctly warns about disks larger than UINT_MAX sectors (2TiB - 512 bytes for 512-byte sectors), but get_disk_ranges() allowed creating partitions that would overflow the 32-bit size field. Addresses: https://issues.redhat.com/browse/RHEL-122367 Signed-off-by: Karel Zak --- diff --git a/libfdisk/src/dos.c b/libfdisk/src/dos.c index db7e25716..c88d2a4f2 100644 --- a/libfdisk/src/dos.c +++ b/libfdisk/src/dos.c @@ -1241,8 +1241,8 @@ static int get_disk_ranges(struct fdisk_context *cxt, int logical, else *last = cxt->total_sectors - 1; - if (*last > UINT_MAX) - *last = UINT_MAX; + if (*last >= UINT_MAX) + *last = UINT_MAX - 1; *first = cxt->first_lba; }