Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To:     maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch,
        sumit.semwal@linaro.org, christian.koenig@amd.com, axboe@kernel.dk,
        oleg@redhat.com, tglx@linutronix.de, dvyukov@google.com,
        walter-zh.wu@mediatek.com
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.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
Subject: [PATCH v3 3/9] drm: check for null master in drm_is_current_master_locked
Date:   Wed, 18 Aug 2021 15:38:18 +0800
Message-Id: <20210818073824.1560124-4-desmondcheongzx@gmail.com>
In-Reply-To: <20210818073824.1560124-1-desmondcheongzx@gmail.com>
References: <20210818073824.1560124-1-desmondcheongzx@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

There is a window after calling drm_master_release, and before a file
is freed, where drm_file can have is_master set to true, but both the
drm_file and drm_device have no master.

This could result in wrongly approving permissions in
drm_is_current_master_locked. Add a check that fpriv->master is
non-NULl to guard against this scenario.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
 drivers/gpu/drm/drm_auth.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 8c0e0dba1611..f9267b21556e 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -66,7 +66,8 @@ static bool drm_is_current_master_locked(struct drm_file *fpriv)
 	lockdep_assert_once(lockdep_is_held(&fpriv->minor->dev->master_lookup_lock) ||
 			    lockdep_is_held(&fpriv->minor->dev->master_mutex));
 
-	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
+	return (fpriv->is_master && fpriv->master &&
+		drm_lease_owner(fpriv->master) == fpriv->minor->dev->master);
 }
 
 /**
-- 
2.25.1