Re: [PATCH] sun disk label: fix signed int usage for sector count

[Jeff Mahoney <jeffm@suse.com>]

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Jan Engelhardt wrote:
>> The current sun disklabel code uses a signed int for the sector count. When
>> partitions larger than 1 TB are used, the cast to a sector_t causes the
>> partition sizes to be invalid:
>>
> 
> Is not it that the sun disklabel does not even support 
> [ptabs/partitions] more than 1 TB?

You're right. The Solaris side of things treats this as signed. I'm not sure how
the user reporting this problem ended up with partitions larger than 1 TB. It
looks like Solaris just treats the entire label as invalid and rejects the whole thing.

I'm not sure how many people out there are using Sun disk labels with sizes > 1TB.
It seems like a pretty rare corner case, but there's no reason any data stored in
those partitions wouldn't be invalid, and it will suddenly cut them off. Is this a
rare enough occurrence that we don't care?

The following patch rejects the partitions, but it would be trivial to switch it
to a warning. I'll post it separately if we agree this is the correct solution.

- -Jeff

 Solaris treats Sun disklabel partition sizes as a signed int, and rejects
 partitions that claim to be larger than 1 TB.

 Linux likewise treats the sector count as a signed int, but doesn't do
 any checking, and passes it to put_partition, which casts it causing it to
 be sign extended.

 This patch performs checking to see if individual partitions are valid, and
 rejects the disk label entirely if they are not.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>

- --- linux-2.6.17/fs/partitions/sun.c	2006-01-02 22:21:10.000000000 -0500
+++ linux-2.6.17.fix/fs/partitions/sun.c	2006-08-26 11:54:54.000000000 -0400
@@ -74,10 +74,18 @@ int sun_partition(struct parsed_partitio
 	spc = be16_to_cpu(label->ntrks) * be16_to_cpu(label->nsect);
 	for (i = 0; i < 8; i++, p++) {
 		unsigned long st_sector;
- -		int num_sectors;
+		unsigned int num_sectors;
 
 		st_sector = be32_to_cpu(p->start_cylinder) * spc;
 		num_sectors = be32_to_cpu(p->num_sectors);
+
+		if (num_sectors > INT_MAX) {
+			printk("Dev %s Sun disklabel: partition %d has "
+			       "invalid size > 1 TB\n", bdevname(bdev, b), i);
+			put_dev_sector(sec);
+			return 0;
+		}
+
 		if (num_sectors) {
 			put_partition(state, slot, st_sector, num_sectors);
 			if (label->infos[i].id == LINUX_RAID_PARTITION)


- -- 
Jeff Mahoney
SUSE Labs
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