Re: [PATCH] vfs: fix IMA lockdep circular locking dependency

From: Eric Paris <eparis@parisplace.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mimi Zohar <zohar@us.ibm.com>,
	linux-security-module@vger.kernel.org,
	Mimi Zohar <zohar@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] vfs: fix IMA lockdep circular locking dependency
Date: Tue, 15 May 2012 15:42:57 -0400	[thread overview]
Message-ID: <CACLa4pujEBAS349Pr-EcBmzQgTHWthhCMV0Yqq0BG-F_gDjz4Q@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyPPZ0wayqPMCZtfP1w9nN-GnKJxYc9i_XM_Qk8d-zJzg@mail.gmail.com>

On Tue, May 15, 2012 at 2:41 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, May 15, 2012 at 10:19 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>>  - move the whole call to security_file_mmap() to outside the
>> mmap_sem, and test the *suggested* address (which is not the same as
>> the final address)
>
> Actually, I think I have a simpler approach.
>
> We already actually have two *different* security_file_mmap() calls:
> it's just that currently the difference is shown by the last argument
> to the function ("addr_only").

I'm the one who introduced that bit of horrific.  I originally did it
the way you describe and someone (it was a long time ago, and I think
it was Ted Tso, but I am probably very very wrong on that) ask me to
tack it on the end like this.  I'd be very happy with the split you
describe.

I'd rather not, however, move the address call site like you described
above, as I don't want to allow NULL + ~MAP_FIXED to be tested until
it has been resolved to a real address.  I don't want someone to find
a way to get the kernel to choose 4096 and avoid the check....

Mimi, would you like to do this (slightly) larger change?  Should I?