[parted-devel] [PATCH] libparted: reallocate buf after _disk_analyse_block_size call

Jim Meyering jim at meyering.net
Thu Sep 6 17:01:29 UTC 2012

Brian C. Lane wrote:
> On Tue, Sep 04, 2012 at 04:51:53PM -0700, Brian C. Lane wrote:
>> I'm looking for comments on this quick test patch. The problem is this:
>> In Fedora we have a hybrid iso that also contains a couple of EFI boot
>> partitions in order to make it bootable on EFI systems and on Apple
>> harware. Parted is sometimes throwing an error when they are written to
>> a USB stick using dd and then examined with 'parted /dev/sdd p' or
>> parted -l
>> I think the right way to fix this is to reallocate the buf with the new
>> size. The only other alternative I can see is to make
>> __disk_analyse_block_size always return an error when there is a
>> mismatch instead of prompting the user.
>> I'm also not sure how we could write a good test case for this.
> On re-reading that I realize I wasn't too clear as to what actually
> happens. When it examines the USB it hits this warning in
> _disk_analyse_block_size:
> Warning: The driver descriptor says the physical block size is 2048
> bytes, but Linux says it is 512 bytes.
> If you tell it to ignore it will change the disk->dev->sector_size to
> 2048, then when it tries to read the ghost partitions in mac_read it
> will overrun the buffer and clobber the heap, which results in the next
> error causing a SIGSEGV as it tries to malloc space for the error
> message.

Thanks for the added detail.
Would you please include something like that to the commit log
for your patch?

Re testing, would it be enough to use parted to create a MAC partition
table with "mklabel mac", add at least one partition, and then use dd or
perl to poke a new, larger number into its 16-bit big-endian
raw_disk->block_size field ?

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