Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Sat, 2 Apr 2016 11:46:34 -0400
From: Theodore Ts'o <>
To: Yves-Alexis Perez <>
Cc:, Johannes Segitz <>,
	Ben Hutchings <>
Subject: Re: ext4 data corruption due to punch hole races

On Sat, Apr 02, 2016 at 03:14:57PM +0200, Yves-Alexis Perez wrote:
> > "When punching holes into a file races with the page fault of the same
> > area, it is possible that freed blocks remain referenced from page cache
> > pages mapped to process' address space. Thus modification of these blocks
> > can corrupt data someone else is now storing in those blocks (which
> > obviously has security implications if you can trick filesystem into
> > storing some important file in those blocks).
> > 
> > This affects all the kernels where we support ext4 for writing. Relevant
> > fixes upstream are commits ea3d7209ca01da209cda6f0dea8be9cc4b7a933b,
> > 17048e8a083fec7ad841d88ef0812707fbc7e39f,
> > 32ebffd3bbb4162da5ff88f9a35dd32d0a28ea70,
> > 011278485ecc3cd2a3954b5d4c73101d919bf1fa."
> any reason why those commits weren't CC: stable? If this really affects all
> kernels where ext4 writing is possible, that means basically all current
> stable kernels more or less, I guess?

They weren't cc'ed stable because they're fairly complex patches,
which (a) means they probably wouldn't auto-apply anyway, and (b)
someone who does do the (probably manual) back port they would be
*very* strongly advised to run them through a complete ext4 regression
test series[1] to make sure the patches actually don't make things
worse from a stability perspective.


I do spend *small* amount of work testing the stable kernels (3.10,
3.14, 3.18, 4.1, 4.4) using gce-xfstests and backporting and testing
patches that weren't cc'ed to stable for various reasons.  It's a
pretty low priority task, though, and I'd really love to delegate this
to someone else.  I just don't have the bandwidth to support back
level kernels (this is why distributions get paid the big bucks), and
note that even if I or someone else stepped up, this won't necessarily
help Debian, which isn't on a one of the stable kernel versions.

If anyone is interested, please contact me.  Otherwise, I'll get to it

						- Ted

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.