linux-kernel - Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm

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Date:   Wed, 24 Aug 2022 17:50:43 +0000
From:   Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To:     Juergen Gross <jgross@...e.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Stefano Stabellini <sstabellini@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Rustam Subkhankulov <subkhankulov@...ras.ru>
Subject: Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()


On 24.08.22 17:26, Juergen Gross wrote:

Hello Juergen

> The error exit of privcmd_ioctl_dm_op() is calling unlock_pages()
> potentially with pages being NULL, leading to a NULL dereference.
>
> Fix that by calling unlock_pages only if lock_pages() was at least
> partially successful.
>
> Cc: <stable@...r.kernel.org>
> Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
> Reported-by: Rustam Subkhankulov <subkhankulov@...ras.ru>
> Signed-off-by: Juergen Gross <jgross@...e.com>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>


> ---
>   drivers/xen/privcmd.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 3369734108af..ec87968b4459 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -679,7 +679,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>   	rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
>   	if (rc < 0) {
>   		nr_pages = pinned;
> -		goto out;
> +		goto unlock;
>   	}
>   
>   	for (i = 0; i < kdata.num; i++) {
> @@ -691,8 +691,9 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
>   	rc = HYPERVISOR_dm_op(kdata.dom, kdata.num, xbufs);
>   	xen_preemptible_hcall_end();
>   
> -out:
> + unlock:
>   	unlock_pages(pages, nr_pages);
> + out:
>   	kfree(xbufs);
>   	kfree(pages);
>   	kfree(kbufs);

-- 
Regards,

Oleksandr Tyshchenko