linux-kernel - Re: [PATCH] kvm: Prevent kvm_init from corrupting debugfs structures

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Message-ID: <20091015160423.GC9629@amt.cnet>
Date:	Thu, 15 Oct 2009 13:04:23 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Avi Kivity <avi@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH] kvm: Prevent kvm_init from corrupting debugfs
	structures

On Wed, Oct 14, 2009 at 04:21:00PM -0700, Darrick J. Wong wrote:
> I'm seeing an oops condition when kvm-intel and kvm-amd are modprobe'd
> during boot (say on an Intel system) and then rmmod'd:
> 
>    # modprobe kvm-intel
>      kvm_init()
>      kvm_init_debug()
>      kvm_arch_init()  <-- stores debugfs dentries internally
>      (success, etc)
> 
>    # modprobe kvm-amd
>      kvm_init()
>      kvm_init_debug() <-- second initialization clobbers kvm's
>                           internal pointers to dentries
>      kvm_arch_init()
>      kvm_exit_debug() <-- and frees them
> 
>    # rmmod kvm-intel
>      kvm_exit()
>      kvm_exit_debug() <-- double free of debugfs files!
> 
>      *BOOM*
> 
> If execution gets to the end of kvm_init(), then the calling module has been
> established as the kvm provider.  Move the debugfs initialization to the end of
> the function, and remove the now-unnecessary call to kvm_exit_debug() from the
> error path.  That way we avoid trampling on the debugfs entries and freeing
> them twice.
> 
> Signed-off-by: Darrick J. Wong <djwong@...ibm.com>

Applied, thanks.

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