linux-kernel - Re: next-20130117 - kernel BUG with aio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130124221352.GK26407@google.com>
Date:	Thu, 24 Jan 2013 14:13:52 -0800
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, jack@...e.cz,
	tytso@....edu
Cc:	Valdis.Kletnieks@...edu, Hillf Danton <dhillf@...il.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	linux-kernel@...r.kernel.org, linux-aio@...ck.org, zab@...bo.net,
	linux-fsdevel@...r.kernel.org
Subject: Re: next-20130117 - kernel BUG with aio

On Thu, Jan 24, 2013 at 01:27:59PM -0800, Andrew Morton wrote:
> Please also take a look at Jan's recent
> http://www.spinics.net/lists/linux-fsdevel/msg61738.html and have a
> think about how this plays with your patchset.

I can't think of any possible interactions - none of my aio stuff messes
with the way the fput() happens; the aio code does call fput() when the
kiocb is freed and my patches do touch _that_ code but none of the
behaviour there changes.

Might be worth documenting this though, I can't think of any reason it'd
be obvious looking at the aio code that the fput() has to happen after
aio_complete(). As with the bugs I just sent you patches for it's not
terribly clear who owns what in the kiocb when.

Reading those patches though - the main change is to call
inode_dio_done() before calling aio_complete(). All inode_dio_done()
does though is issue a wakeup - to whatever called inode_dio_wait().

That means whatever called inode_dio_wait() needs its own ref on the
inode, and from a cursory glance at the code it is _not_ at all clear to
me that's the case - if inode_dio_wait() is merely finishing things for
that specific IO that need to be done in process context, I can easily
imagine it not being the case.

Assuming whatever does call inode_dio_wait() does have its own ref,
there was only a real use after free when nothing was waiting on the
inode.

Similarly for the ext4 code to write unwritten extents - and having seen
and helped chase a bug in that code before, that code _definitely_ needs
auditing.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/