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From:   Cornelia Huck <cohuck@redhat.com>
To:     Schspa Shi <schspa@gmail.com>, alex.williamson@redhat.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        zhaohui.shi@horizon.ai, Schspa Shi <schspa@gmail.com>
Subject: Re: [PATCH] vfio: Fix double free for caps->buf
In-Reply-To: <20220628050711.74945-1-schspa@gmail.com>
Organization: Red Hat GmbH
References: <20220628050711.74945-1-schspa@gmail.com>
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Date:   Tue, 28 Jun 2022 10:17:52 +0200
Message-ID: <8735fpcibz.fsf@redhat.com>
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On Tue, Jun 28 2022, Schspa Shi <schspa@gmail.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@gmail.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);
>  	}