linux-kernel - Re: [PATCH][next] nouveau/svm: Fix missing failure check on call to make_device_exclusive

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Date:   Thu, 27 May 2021 10:30:34 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     Colin King <colin.king@...onical.com>
CC:     Ben Skeggs <bskeggs@...hat.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <dri-devel@...ts.freedesktop.org>, <nouveau@...ts.freedesktop.org>,
        <kernel-janitors@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next] nouveau/svm: Fix missing failure check on call to make_device_exclusive_range

On Thursday, 27 May 2021 12:04:59 AM AEST Colin King wrote:
> The call to make_device_exclusive_range can potentially fail leaving
> pointer page not initialized that leads to an uninitialized pointer
> read issue. Fix this by adding a check to see if the call failed and
> returning the error code.
> 
> Addresses-Coverity: ("Uninitialized pointer read")
> Fixes: c620bba9828c ("nouveau/svm: implement atomic SVM access")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
> b/drivers/gpu/drm/nouveau/nouveau_svm.c index 84726a89e665..b913b4907088
> 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -609,8 +609,10 @@ static int nouveau_atomic_range_fault(struct
> nouveau_svmm *svmm,
> 
>                 notifier_seq = mmu_interval_read_begin(&notifier->notifier);
> mmap_read_lock(mm);
> -               make_device_exclusive_range(mm, start, start + PAGE_SIZE,
> -                                           &page, drm->dev);
> +               ret = make_device_exclusive_range(mm, start, start +
> PAGE_SIZE, +                                                 &page,
> drm->dev); +               if (ret < 0)
> +                       goto out;

Thanks for spotting, this is fixing get_user_pages() inside 
make_device_exclusive_range() returning an error. However the check needs to 
happen after dropping mmap_lock below:

>                 mmap_read_unlock(mm);
>                 if (!page) {
>                         ret = -EINVAL;
> --
> 2.31.1