linux-kernel - Re: [PATCH] vfio: Fix double free for caps->buf

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Date:   Tue, 28 Jun 2022 10:17:52 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Schspa Shi <schspa@...il.com>, alex.williamson@...hat.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhaohui.shi@...izon.ai, Schspa Shi <schspa@...il.com>
Subject: Re: [PATCH] vfio: Fix double free for caps->buf

On Tue, Jun 28 2022, Schspa Shi <schspa@...il.com> wrote:

> There is a double free, if vfio_iommu_dma_avail_build_caps
> calls failed.
>
> The following call path will call vfio_info_cap_add multiple times
>
> vfio_iommu_type1_get_info
> 	if (!ret)
> 		ret = vfio_iommu_dma_avail_build_caps(iommu, &caps);
>
> 	if (!ret)
> 		ret = vfio_iommu_iova_build_caps(iommu, &caps);
>
> If krealloc failed on vfio_info_cap_add, there will be a double free.

But it will only call it several times if the last call didn't fail,
won't it?

>
> Signed-off-by: Schspa Shi <schspa@...il.com>
> ---
>  drivers/vfio/vfio.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 61e71c1154be..a0fb93866f61 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1812,6 +1812,7 @@ struct vfio_info_cap_header *vfio_info_cap_add(struct vfio_info_cap *caps,
>  	buf = krealloc(caps->buf, caps->size + size, GFP_KERNEL);
>  	if (!buf) {
>  		kfree(caps->buf);
> +		caps->buf = NULL;

We could add this as some kind of hardening, I guess. Current callers
all seem to deal with failure correctly.

>  		caps->size = 0;
>  		return ERR_PTR(-ENOMEM);
>  	}