linux-kernel - Re: [PATCH 2/2] ppc: kvm: use anon_inode_getfd() with O

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Date:	Mon, 26 Aug 2013 09:39:14 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Alexander Graf <agraf@...e.de>
CC:	Yann Droneaud <ydroneaud@...eya.com>,
	Gleb Natapov <gleb@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ppc: kvm: use anon_inode_getfd() with O_CLOEXEC flag

Il 25/08/2013 17:04, Alexander Graf ha scritto:
> 
> On 24.08.2013, at 21:14, Yann Droneaud wrote:
> 
>> KVM uses anon_inode_get() to allocate file descriptors as part
>> of some of its ioctls. But those ioctls are lacking a flag argument
>> allowing userspace to choose options for the newly opened file descriptor.
>>
>> In such case it's advised to use O_CLOEXEC by default so that
>> userspace is allowed to choose, without race, if the file descriptor
>> is going to be inherited across exec().
>>
>> This patch set O_CLOEXEC flag on all file descriptors created
>> with anon_inode_getfd() to not leak file descriptors across exec().
>>
>> Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
>> Link: http://lkml.kernel.org/r/cover.1377372576.git.ydroneaud@opteya.com
> 
> Reviewed-by: Alexander Graf <agraf@...e.de>
> 
> Would it make sense to simply inherit the O_CLOEXEC flag from the
> parent kvm fd instead? That would give user space the power to keep
> fds across exec() if it wants to.

Does it make sense to use non-O_CLOEXEC file descriptors with KVM at
all?  Besides fork() not being supported by KVM, as described in
Documentation/virtual/kvm/api.txt, the VMAs of the parent process go
away as soon as you exec().  I'm not sure how you can use the inherited
file descriptor in a sensible way after exec().

Paolo
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