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

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Date:   Thu, 25 Aug 2022 09:38:52 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        stable@...r.kernel.org,
        Rustam Subkhankulov <subkhankulov@...ras.ru>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

On 24.08.2022 16:26, Juergen Gross wrote:
> 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: Jan Beulich <jbeulich@...e.com>
albeit I wonder whether you did consider the variant actually
reducing code size (and avoiding the need for yet another label),
...

> --- 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;

... dropping this line and ...

> -		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);

... passing "pinned" here.

Jan

> + out:
>  	kfree(xbufs);
>  	kfree(pages);
>  	kfree(kbufs);