2022-10-14 08:05:49

by Hou Wenlong

Subject: [PATCH] KVM: x86: Reduce refcount if single_open() fails in kvm_mmu_rmaps_stat_open()

Refcount is increased before calling single_open() in
kvm_mmu_rmaps_stat_open(), If single_open() fails, refcount should be
restored, otherwise the vm couldn't be destroyed.

Fixes: 3bcd0662d66fd ("KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file")
Signed-off-by: Hou Wenlong <[email protected]>
---
arch/x86/kvm/debugfs.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
index cfed36aba2f7..412ed1b341fa 100644
--- a/arch/x86/kvm/debugfs.c
+++ b/arch/x86/kvm/debugfs.c
@@ -162,7 +162,12 @@ static int kvm_mmu_rmaps_stat_open(struct inode *inode, struct file *file)
if (!kvm_get_kvm_safe(kvm))
return -ENOENT;

- return single_open(file, kvm_mmu_rmaps_stat_show, kvm);
+ if (single_open(file, kvm_mmu_rmaps_stat_show, kvm)) {
+ kvm_put_kvm(kvm);
+ return -ENOMEM;
+ }
+
+ return 0;
}

static int kvm_mmu_rmaps_stat_release(struct inode *inode, struct file *file)
--
2.31.1

2022-10-14 14:26:22

by Peter Xu

Subject: Re: [PATCH] KVM: x86: Reduce refcount if single_open() fails in kvm_mmu_rmaps_stat_open()

On Fri, Oct 14, 2022 at 03:55:11PM +0800, Hou Wenlong wrote:
> Refcount is increased before calling single_open() in
> kvm_mmu_rmaps_stat_open(), If single_open() fails, refcount should be
> restored, otherwise the vm couldn't be destroyed.
>
> Fixes: 3bcd0662d66fd ("KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file")
> Signed-off-by: Hou Wenlong <[email protected]>
> ---
> arch/x86/kvm/debugfs.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> index cfed36aba2f7..412ed1b341fa 100644
> --- a/arch/x86/kvm/debugfs.c
> +++ b/arch/x86/kvm/debugfs.c
> @@ -162,7 +162,12 @@ static int kvm_mmu_rmaps_stat_open(struct inode *inode, struct file *file)
> if (!kvm_get_kvm_safe(kvm))
> return -ENOENT;
>
> - return single_open(file, kvm_mmu_rmaps_stat_show, kvm);
> + if (single_open(file, kvm_mmu_rmaps_stat_show, kvm)) {
> + kvm_put_kvm(kvm);
> + return -ENOMEM;
> + }

Thanks for fixing this. Would it be nicer to wire the single_open retval
(even though it'll only fail with -ENOMEM with current code base)?

--
Peter Xu

2022-10-17 03:04:33

by Hou Wenlong

Subject: Re: [PATCH] KVM: x86: Reduce refcount if single_open() fails in kvm_mmu_rmaps_stat_open()

On Fri, Oct 14, 2022 at 10:09:55PM +0800, Peter Xu wrote:
> On Fri, Oct 14, 2022 at 03:55:11PM +0800, Hou Wenlong wrote:
> > Refcount is increased before calling single_open() in
> > kvm_mmu_rmaps_stat_open(), If single_open() fails, refcount should be
> > restored, otherwise the vm couldn't be destroyed.
> >
> > Fixes: 3bcd0662d66fd ("KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file")
> > Signed-off-by: Hou Wenlong <[email protected]>
> > ---
> > arch/x86/kvm/debugfs.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> > index cfed36aba2f7..412ed1b341fa 100644
> > --- a/arch/x86/kvm/debugfs.c
> > +++ b/arch/x86/kvm/debugfs.c
> > @@ -162,7 +162,12 @@ static int kvm_mmu_rmaps_stat_open(struct inode *inode, struct file *file)
> > if (!kvm_get_kvm_safe(kvm))
> > return -ENOENT;
> >
> > - return single_open(file, kvm_mmu_rmaps_stat_show, kvm);
> > + if (single_open(file, kvm_mmu_rmaps_stat_show, kvm)) {
> > + kvm_put_kvm(kvm);
> > + return -ENOMEM;
> > + }
>
> Thanks for fixing this. Would it be nicer to wire the single_open retval
> (even though it'll only fail with -ENOMEM with current code base)?
>
I agree, it would be nicer to return the single_open() retval directly.
I just follow how failure of simple_attr_open() is handled in kvm_debugfs_open(),
but I think it should be changed too.

> --
> Peter Xu