fs/partition/msdos: fix unusable extended partition for > 512B sector

Smaller size than a minimum blocksize can't be used, after all it's
handled like 0 size.

For extended partition itself, this makes sure to use bigger size than one
logical sector size at least.
Signed-off-by: NOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Daniel Taylor <Daniel.Taylor@wdc.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/partitions/msdos.c

@@ -492,9 +492,16 @@ int msdos_partition(struct parsed_partitions *state, struct block_device *bdev)
 		if (!size)
 			continue;
 		if (is_extended_partition(p)) {
-			/* prevent someone doing mkfs or mkswap on an
-			   extended partition, but leave room for LILO */
-			put_partition(state, slot, start, size == 1 ? 1 : 2);
+			/*
+			 * prevent someone doing mkfs or mkswap on an
+			 * extended partition, but leave room for LILO
+			 * FIXME: this uses one logical sector for > 512b
+			 * sector, although it may not be enough/proper.
+			 */
+			sector_t n = 2;
+			n = min(size, max(sector_size, n));
+			put_partition(state, slot, start, n);
+
 			printk(" <");
 			parse_extended(state, bdev, start, size);
 			printk(" >");