From 848018183869d908ddfa59ce7362272f65baa860 Mon Sep 17 00:00:00 2001 From: Tobias Stoeckmann Date: Sat, 27 Aug 2016 19:28:16 +0200 Subject: libfdisk: Fix assert error in free space handling An off-by-one issue exists in fdisk_get_freespaces. It can trigger an assert, as seen here: $ dd if=/dev/zero of=cfdisk.iso bs=1M count=1 $ losetup -f cfdisk.iso $ echo w | fdisk /dev/loop0 $ echo '1,2' | sfdisk /dev/loop0 --append $ echo '3,' | sfdisk /dev/loop0 --append $ sfdisk --list-free /dev/loop0 Aborted $ _ Problem here is an invalid "grain" processing. A grain is considered expected free space between partitions which can be required for proper alignment. Normally, it's 1 MB but in this case our iso is merely 1 MB so the grain is reduced to 1 byte. The if-condition in question checks for "last + grain <= pa->start" and therefore even triggers if there is no space between them (due to equal check). Eventually, the start block address is higher than the end block address which triggers the assert(). Signed-off-by: Tobias Stoeckmann --- libfdisk/src/table.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'libfdisk') diff --git a/libfdisk/src/table.c b/libfdisk/src/table.c index 755c6c286..bf30d1b19 100644 --- a/libfdisk/src/table.c +++ b/libfdisk/src/table.c @@ -616,7 +616,7 @@ int fdisk_get_freespaces(struct fdisk_context *cxt, struct fdisk_table **tb) /* We ignore small free spaces (smaller than grain) to keep partitions * aligned, the exception is space before the first partition where * we assume that cxt->first_lba is aligned. */ - if (last + grain <= pa->start + if (last + grain < pa->start || (last < pa->start && last == cxt->first_lba)) { rc = table_add_freespace(cxt, *tb, last + (last > cxt->first_lba ? 1 : 0), -- cgit v1.2.3-55-g7522