linux-kernel - Re: [PATCH v4] xen/privcmd: fix error exit of privcmd_ioctl_dm

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Date:   Thu, 25 Aug 2022 16:37:27 +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 v4] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

On 25.08.2022 16:19, 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.
> 
> Additionally lock_pages() doesn't check for pin_user_pages_fast()
> having been completely successful, resulting in potentially not
> locking all pages into memory. This could result in sporadic failures
> when using the related memory in user mode.
> 
> Fix all of that by calling unlock_pages() always with the real number
> of pinned pages, which will be zero in case pages being NULL, and by
> checking the number of pages pinned by pin_user_pages_fast() matching
> the expected number of pages.
> 
> 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>