linux-kernel - Re: drm: Add missing field copy in compat_drm

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Date:   Thu, 13 Jul 2017 10:20:20 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>,
        linux-kernel@...r.kernel.org
CC:     briannorris@...omium.org, dianders@...omium.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Sean Paul <seanpaul@...omium.org>
Subject: Re: drm: Add missing field copy in compat_drm_version

Hi guys,

i was testing this on arm64 base chromeos(with arm32 userspace).

and the libdrm crashed:
     drmVersionPtr drmGetVersion(int fd)
     {
     ...
         memclear(*version);

         if (drmIoctl(fd, DRM_IOCTL_VERSION, version)) {
     ...
         if (version->name_len)
             version->name    = drmMalloc(version->name_len + 1); <-- 
rely on the lengths updated by kernel
         if (version->date_len)
             version->date    = drmMalloc(version->date_len + 1);
         if (version->desc_len)
             version->desc    = drmMalloc(version->desc_len + 1);
     ...
         if (version->name_len) version->name[version->name_len] = '\0'; 
<-- crashed here, since the name_len would always be zero, so 
version->name would be nullptr.


On 07/12/2017 02:18 PM, Jeffy Chen wrote:
> DRM_IOCTL_VERSION is supposed to update the name_len/date_len/desc_len
> fields to user.
>
> Fixes: 012c6741c6aa("switch compat_drm_version() to drm_ioctl_kernel()")
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> ---
>
>   drivers/gpu/drm/drm_ioc32.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_ioc32.c b/drivers/gpu/drm/drm_ioc32.c
> index 94acf51..2789356 100644
> --- a/drivers/gpu/drm/drm_ioc32.c
> +++ b/drivers/gpu/drm/drm_ioc32.c
> @@ -112,6 +112,9 @@ static int compat_drm_version(struct file *file, unsigned int cmd,
>   	v32.version_major = v.version_major;
>   	v32.version_minor = v.version_minor;
>   	v32.version_patchlevel = v.version_patchlevel;
> +	v32.name_len = v.name_len;
> +	v32.date_len = v.date_len;
> +	v32.desc_len = v.desc_len;
>   	if (copy_to_user((void __user *)arg, &v32, sizeof(v32)))
>   		return -EFAULT;
>   	return 0;
>
>