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From:   Eugene Korenevsky <ekorenevsky@gmail.com>
Date:   Sat, 6 Oct 2018 21:41:27 +0300
Message-ID: <CAJC2YLYqb6WB43P5pJe=D7GXgUY16PS=QLVJbD8=qEH=aB9qvg@mail.gmail.com>
Subject: Re: [PATCH v2] efi: take size of partition entry from GPT header
To:     kzak@redhat.com
Cc:     David.Laight@aculab.com, Davidlohr Bueso <dave@stgolabs.net>,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>
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> is_gpt_valid() already contains
>         pt_size = (u64)le32_to_cpu((*gpt)->num_partition_entries) *
>                 le32_to_cpu((*gpt)->sizeof_partition_entry);
>         if (pt_size > KMALLOC_MAX_SIZE)
>                 pr_debug("GUID Partition Table is too large: %llu > %lu bytes\n",
>                 (unsigned long long)pt_size, KMALLOC_MAX_SIZE);
>                 goto fail;
>         }
> I guess it good enough for sanity check.
>
> If you want to be really paranoid than you can also check that array
> is possible to store to the expected area on the disk:
>
>     pt_size <= (gpt->first_usable_lba - gpt->partition_entry_lba)
>

Well, we should apply several checks for different cases:
- primary GPT: table entries should not override gpt->first_usable_lba
- alternate GPT, table entries BEFORE agpt (agpt->partition_entry_lba
< agpt_lba): table entries should not override agpt_lba AND
agpt->partition_entry_lba MUST BE more than agpt->last_usable_lba
- alternate GPT, table entries AFTER agpt (agpt->partition_entry_lba >
agpt_lba): table entries should not override the end of the disk

Is this correct?

--
Eugene