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SubjectRe: Corrupt file-system(s) leads to crash
From
   Date: 	Mon, 6 Apr 1998 21:34:35 -0400 (EDT)
From: "Albert D. Cahalan" <acahalan@cs.uml.edu>

Some people are reporting related troubles with corrupted partition
tables getting even more corrupted:

1. fdisk puts extended partition info _in_ the previous partition
2. mke2fs does not sanity check
3. the kernel partition code does not sanity check
4. somebody fills up the filesystem
5. goodbye partitions!

It's not as serious as your disk destruction, but the solution is
the same. Partition size and location must be sanity checked when
the partition table is read. Partition access must be bounds checked.

Partition access are bounds checked. The problem was that the partition
bounds were incorrect. We could say that the kernel partition code
should have done that sanity check, but there are even potentially times
when overlapping partitions is the right thing.

The real problem is that some versions of fdisk, when creating
non-contiguous extended partitions, can create overlapping partitions
when the user didn't request it. This is a real bug, and given that
there's known bad versions of fdisk out there, it might make sense to
try to detect that, especially in the kernel code which reads partition
tables.

Having mke2fs do the sanity check would be a nasty abstraction
violation, and there isn't even a good way to do it, short of having
mke2fs read the partition label itself. Currently mke2fs and the rest
of e2fsprogs tools suite are partition label independent. If you want
to use a BSD disk label instead of the standard partition table, you can
do so, and the ext2 tools will work just fine. On an Sparcstation, if
you want to use a Solaris compatible disk label, that will work fine
too. So having mke2fs do the sanity check would force it to be
partition label specific, and it's not at all clear this would be a good
thing to do....
- Ted


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