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

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Message-ID: <4AD6CB42.5040006@redhat.com>
Date:	Thu, 15 Oct 2009 16:12:02 +0900
From:	Avi Kivity <avi@...hat.com>
To:	djwong@...ibm.com
CC:	Marcelo Tosatti <mtosatti@...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 10/15/2009 08:21 AM, 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.
>
>    

Looks good.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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