linux-kernel - Re: [PATCH v1] vfs: fix IMA lockdep circular locking dependency

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Date:	Tue, 24 Jan 2012 13:40:50 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-security-module@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Mimi Zohar <zohar@...ibm.com>
Subject: Re: [PATCH v1] vfs: fix IMA lockdep circular locking dependency

On Tue, 2012-01-24 at 12:45 -0500, Eric Paris wrote:
> On Tue, 2012-01-24 at 12:34 -0500, Mimi Zohar wrote:
> > The circular lockdep is caused by allocating the 'iint' for mmapped
> > files.  Originally when an 'iint' was allocated for every inode
> > in inode_alloc_security(), before the inode was accessible, no
> > locking was necessary.  Commits bc7d2a3e and 196f518 changed this
> > behavior and allocated the 'iint' on a per need basis, resulting in
> > the mmap_sem being taken before the i_mutex for mmapped files.
> > 
> > Possible unsafe locking scenario:
> >        CPU0                    CPU1
> >        ----                    ----
> > lock(&mm->mmap_sem);
> >                               lock(&sb->s_type->i_mutex_key);
> >                               lock(&mm->mmap_sem);
> > lock(&sb->s_type->i_mutex_key);
> > 
> > The existing security_file_mmap() hook is after the mmap_sem is taken.
> > This patch moves the ima_file_mmap() call from security_file_mmap() to
> > prior to the mmap_sem being taken.
> > 
> > Changelog v1:
> > - Instead of just pre-allocating the iint in a new hook, do ALL of the
> > work in the new/moved ima_file_mmap() hook. (Based on Eric Paris' suggestion.)
> > - Removed do_mmap_with_sem() helper function.
> > - export ima_file_mmap()
> 
> Why does it need to be exported?  What module might call this?

Without it, I'm getting:

Kernel: arch/x86/boot/bzImage is ready  (#246)
ERROR: "ima_file_mmap" [arch/x86/ia32/ia32_aout.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2

Mimi

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