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Thu, 26 Aug 2021 04:54:06 -0700 (PDT) Subject: Re: [PATCH v8 1/7] drm: fix null ptr dereference in drm_master_release To: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, sumit.semwal@linaro.org, christian.koenig@amd.com, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, chris@chris-wilson.co.uk, ville.syrjala@linux.intel.com, matthew.auld@intel.com, dan.carpenter@oracle.com, tvrtko.ursulin@intel.com, matthew.d.roper@intel.com, lucas.demarchi@intel.com, karthik.b.s@intel.com, jose.souza@intel.com, manasi.d.navare@intel.com, airlied@redhat.com, aditya.swarup@intel.com, andrescj@chromium.org, linux-graphics-maintainer@vmware.com, zackr@vmware.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org References: <20210826020122.1488002-1-desmondcheongzx@gmail.com> <20210826020122.1488002-2-desmondcheongzx@gmail.com> From: Desmond Cheong Zhi Xi Message-ID: <05f4d472-7a76-598a-e792-a847a3e8516a@gmail.com> Date: Thu, 26 Aug 2021 19:53:58 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/8/21 5:53 pm, Daniel Vetter wrote: > On Thu, Aug 26, 2021 at 10:01:16AM +0800, Desmond Cheong Zhi Xi wrote: >> drm_master_release can be called on a drm_file without a master, which >> results in a null ptr dereference of file_priv->master->magic_map. The >> three cases are: >> >> 1. Error path in drm_open_helper >> 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) >> >> 2. Error path in mock_drm_getfile >> mock_drm_getfile(): >> anon_inode_getfile(); <--- returns error, drm_file.master not set >> drm_file_free(): >> drm_master_release(); <--- NULL ptr dereference >> (file_priv->master->magic_map) >> >> 3. In drm_client_close, as drm_client_open doesn't set up a master >> >> drm_file.master is set up in drm_open_helper through the call to >> drm_master_open, so we mirror it with a call to drm_master_release in >> drm_close_helper, and remove drm_master_release from drm_file_free to >> avoid the null ptr dereference. >> >> Signed-off-by: Desmond Cheong Zhi Xi > > Reviewed-by: Daniel Vetter > > I guess we should also have a cc: stable on this one? I think this bug > existed since pretty much forever, but maybe more prominent with the > drm_client stuff added a while ago. > -Daniel > Thanks for the reviews, Daniel. Took a closer look. I think if we cc: stable, this fix should accompany commit 7eeaeb90a6a5 ("drm/file: Don't set master on in-kernel clients") which moves the drm_master_open out from drm_file_alloc into drm_open_helper. >> --- >> drivers/gpu/drm/drm_file.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c >> index ed25168619fc..90b62f360da1 100644 >> --- a/drivers/gpu/drm/drm_file.c >> +++ b/drivers/gpu/drm/drm_file.c >> @@ -282,9 +282,6 @@ void drm_file_free(struct drm_file *file) >> >> drm_legacy_ctxbitmap_flush(dev, file); >> >> - if (drm_is_primary_client(file)) >> - drm_master_release(file); >> - >> if (dev->driver->postclose) >> dev->driver->postclose(dev, file); >> >> @@ -305,6 +302,9 @@ static void drm_close_helper(struct file *filp) >> list_del(&file_priv->lhead); >> mutex_unlock(&dev->filelist_mutex); >> >> + if (drm_is_primary_client(file_priv)) >> + drm_master_release(file_priv); >> + >> drm_file_free(file_priv); >> } >> >> -- >> 2.25.1 >> >