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From: Daniel Vetter <daniel@ffwll.ch>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Cc: "Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Maxime Ripard" <mripard@kernel.org>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"Dave Airlie" <airlied@linux.ie>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Jens Axboe" <axboe@kernel.dk>, "Oleg Nesterov" <oleg@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	walter-zh.wu@mediatek.com,
	dri-devel <dri-devel@lists.freedesktop.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>,
	"Shuah Khan" <skhan@linuxfoundation.org>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl}
Date: Wed, 18 Aug 2021 18:33:24 +0200	[thread overview]
Message-ID: <CAKMK7uG+nqnkNd56WPhze3V=e1ioL0PTLQxveBofQT3gNPB9HA@mail.gmail.com> (raw)
In-Reply-To: <53a63ac8-f2de-91f7-4e0f-20b0f3f61d52@gmail.com>

On Wed, Aug 18, 2021 at 5:37 PM Desmond Cheong Zhi Xi
<desmondcheongzx@gmail.com> wrote:
>
> On 18/8/21 6:11 pm, Daniel Vetter wrote:
> > On Wed, Aug 18, 2021 at 03:38:19PM +0800, Desmond Cheong Zhi Xi wrote:
> >> There are three areas where we dereference struct drm_master without
> >> checking if the pointer is non-NULL.
> >>
> >> 1. drm_getmagic is called from the ioctl_handler. Since
> >> DRM_IOCTL_GET_MAGIC has no ioctl flags, drm_getmagic is run without
> >> any check that drm_file.master has been set.
> >>
> >> 2. Similarly, drm_getunique is called from the ioctl_handler, but
> >> DRM_IOCTL_GET_UNIQUE has no ioctl flags. So there is no guarantee that
> >> drm_file.master has been set.
> >
> > I think the above two are impossible, due to the refcounting rules for
> > struct file.
> >
>
> Right, will drop those two parts from the patch.
>
> >> 3. drm_master_release can also be called without having a
> >> drm_file.master set. Here is one error path:
> >>    drm_open():
> >>      drm_open_helper():
> >>        drm_master_open():
> >>          drm_new_set_master(); <--- returns -ENOMEM,
> >>                                     drm_file.master not set
> >>        drm_file_free():
> >>          drm_master_release(); <--- NULL ptr dereference
> >>                                     (file_priv->master->magic_map)
> >>
> >> Fix these by checking if the master pointers are NULL before use.
> >>
> >> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> >> ---
> >>   drivers/gpu/drm/drm_auth.c  | 16 ++++++++++++++--
> >>   drivers/gpu/drm/drm_ioctl.c |  5 +++++
> >>   2 files changed, 19 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> >> index f9267b21556e..b7230604496b 100644
> >> --- a/drivers/gpu/drm/drm_auth.c
> >> +++ b/drivers/gpu/drm/drm_auth.c
> >> @@ -95,11 +95,18 @@ EXPORT_SYMBOL(drm_is_current_master);
> >>   int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
> >>   {
> >>      struct drm_auth *auth = data;
> >> +    struct drm_master *master;
> >>      int ret = 0;
> >>
> >>      mutex_lock(&dev->master_mutex);
> >> +    master = file_priv->master;
> >> +    if (!master) {
> >> +            mutex_unlock(&dev->master_mutex);
> >> +            return -EINVAL;
> >> +    }
> >> +
> >>      if (!file_priv->magic) {
> >> -            ret = idr_alloc(&file_priv->master->magic_map, file_priv,
> >> +            ret = idr_alloc(&master->magic_map, file_priv,
> >>                              1, 0, GFP_KERNEL);
> >>              if (ret >= 0)
> >>                      file_priv->magic = ret;
> >> @@ -355,8 +362,12 @@ void drm_master_release(struct drm_file *file_priv)
> >>
> >>      mutex_lock(&dev->master_mutex);
> >>      master = file_priv->master;
> >> +
> >> +    if (!master)
> >> +            goto unlock;
> >
> > This is a bit convoluted, since we're in the single-threaded release path
> > we don't need any locking for file_priv related things. Therefore we can
> > pull the master check out and just directly return.
> >
> > But since it's a bit surprising maybe a comment that this can happen when
> > drm_master_open in drm_open_helper fails?
> >
>
> Sounds good. This can actually also happen in the failure path of
> mock_drm_getfile if anon_inode_getfile fails. I'll leave a short note
> about both of them.
>
> > Another option, and maybe cleaner, would be to move the drm_master_release
> > from drm_file_free into drm_close_helper. That would be fully symmetrical
> > and should also fix the bug here?
> > -Daniel
> >
> Hmmm maybe the first option to move the check out of the lock might be
> better. If I'm not wrong, we would otherwise also need to move
> drm_master_release into drm_client_close.

Do we have to?

If I haven't missed anything, the drm_client stuff only calls
drm_file_alloc and doesn't set up a master. So this should work?
-Daniel

>
> >
> >> +
> >>      if (file_priv->magic)
> >> -            idr_remove(&file_priv->master->magic_map, file_priv->magic);
> >> +            idr_remove(&master->magic_map, file_priv->magic);
> >>
> >>      if (!drm_is_current_master_locked(file_priv))
> >>              goto out;
> >> @@ -379,6 +390,7 @@ void drm_master_release(struct drm_file *file_priv)
> >>              drm_master_put(&file_priv->master);
> >>              spin_unlock(&dev->master_lookup_lock);
> >>      }
> >> +unlock:
> >>      mutex_unlock(&dev->master_mutex);
> >>   }
> >>
> >> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> >> index 26f3a9ede8fe..4d029d3061d9 100644
> >> --- a/drivers/gpu/drm/drm_ioctl.c
> >> +++ b/drivers/gpu/drm/drm_ioctl.c
> >> @@ -121,6 +121,11 @@ int drm_getunique(struct drm_device *dev, void *data,
> >>
> >>      mutex_lock(&dev->master_mutex);
> >>      master = file_priv->master;
> >> +    if (!master) {
> >> +            mutex_unlock(&dev->master_mutex);
> >> +            return -EINVAL;
> >> +    }
> >> +
> >>      if (u->unique_len >= master->unique_len) {
> >>              if (copy_to_user(u->unique, master->unique, master->unique_len)) {
> >>                      mutex_unlock(&dev->master_mutex);
> >> --
> >> 2.25.1
> >>
> >
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

  reply	other threads:[~2021-08-18 16:35 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18  7:38 [PATCH v3 0/9] drm, kernel: update locking for DRM Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 1/9] drm: move master_lookup_lock into drm_device Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master Desmond Cheong Zhi Xi
2021-08-18 10:05   ` Daniel Vetter
2021-08-18 14:50     ` Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 3/9] drm: check for null master in drm_is_current_master_locked Desmond Cheong Zhi Xi
2021-08-18 10:04   ` Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth,ioctl} Desmond Cheong Zhi Xi
2021-08-18 10:11   ` Daniel Vetter
2021-08-18 15:37     ` Desmond Cheong Zhi Xi
2021-08-18 16:33       ` Daniel Vetter [this message]
2021-08-19  5:31         ` [Intel-gfx] [PATCH v3 4/9] drm: fix potential null ptr dereferences in drm_{auth, ioctl} Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 5/9] drm: protect magic_map,unique{_len} with master_lookup_lock Desmond Cheong Zhi Xi
2021-08-18 10:43   ` Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 6/9] drm: convert drm_device.master_mutex into a rwsem Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 7/9] drm: update global mutex lock in the ioctl handler Desmond Cheong Zhi Xi
2021-08-18 11:02   ` Daniel Vetter
2021-08-19 10:52     ` Desmond Cheong Zhi Xi
2021-08-19 11:21       ` [Intel-gfx] " Daniel Vetter
2021-08-18  7:38 ` [PATCH v3 8/9] kernel: export task_work_add Desmond Cheong Zhi Xi
2021-08-18 11:06   ` Daniel Vetter
2021-08-19  9:26   ` Christoph Hellwig
2021-08-19  9:40     ` Desmond Cheong Zhi Xi
2021-08-18  7:38 ` [PATCH v3 9/9] drm: avoid races with modesetting rights Desmond Cheong Zhi Xi

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