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Fri, 03 Jan 2020 12:35:14 -0800 (PST) Received: from dhcp-10-20-1-90.bss.redhat.com ([144.121.20.162]) by smtp.gmail.com with ESMTPSA id h28sm16911014qkk.48.2020.01.03.12.35.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jan 2020 12:35:13 -0800 (PST) Message-ID: Subject: Re: [PATCH] drm/dp_mst: Avoid NULL pointer dereference From: Lyude Paul To: Wayne Lin , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org Date: Fri, 03 Jan 2020 15:35:12 -0500 In-Reply-To: <20191226023151.5448-1-Wayne.Lin@amd.com> References: <20191226023151.5448-1-Wayne.Lin@amd.com> Organization: Red Hat User-Agent: Evolution 3.34.2 (3.34.2-1.fc31) MIME-Version: 1.0 X-MC-Unique: e2SmyAebPHGQs_lxpudNjg-1 X-Mimecast-Spam-Score: 0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jerry.zuo@amd.com, mikita.lipski@amd.com, Nicholas.Kazlauskas@amd.com, stable@vger.kernel.org Content-Type: text/plain; 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Fri, 03 Jan 2020 12:35:14 -0800 (PST) X-Google-Smtp-Source: APXvYqzgi68keBLcjfBEz4zN/KMDnPfwz3LFg1QJoD7HQRJG4uxuW/u3P8yGx/4EeO57ZnsZsWnpOw== X-Received: by 2002:ad4:5421:: with SMTP id g1mr68023134qvt.57.1578083714480; Fri, 03 Jan 2020 12:35:14 -0800 (PST) Received: from dhcp-10-20-1-90.bss.redhat.com ([144.121.20.162]) by smtp.gmail.com with ESMTPSA id h28sm16911014qkk.48.2020.01.03.12.35.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jan 2020 12:35:13 -0800 (PST) Message-ID: Subject: Re: [PATCH] drm/dp_mst: Avoid NULL pointer dereference From: Lyude Paul To: Wayne Lin , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org Cc: Nicholas.Kazlauskas@amd.com, harry.wentland@amd.com, mikita.lipski@amd.com, jerry.zuo@amd.com, stable@vger.kernel.org Date: Fri, 03 Jan 2020 15:35:12 -0500 In-Reply-To: <20191226023151.5448-1-Wayne.Lin@amd.com> References: <20191226023151.5448-1-Wayne.Lin@amd.com> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.2 (3.34.2-1.fc31) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Back from the holidays! Reviewed-by: Lyude Paul Do you need me to push this to drm-misc? On Thu, 2019-12-26 at 10:31 +0800, Wayne Lin wrote: > [Why] > Found kernel NULL pointer dereference under the below situation: > > src — HDMI_Monitor src — HDMI_Monitor > e.g.: \ => > MSTB — MSTB (unplug) MSTB — MSTB > > When display 1 HDMI and 2 DP daisy chain monitors, unplugging the dp > cable connected to source causes kernel NULL pointer dereference at > drm_dp_mst_atomic_check_bw_limit(). When calculating pbn_limit, if > branch is null, accessing "&branch->ports" causes the problem. > > [How] > Judge branch is null or not at the beginning. If it is null, return 0. > > Signed-off-by: Wayne Lin > Cc: stable@vger.kernel.org > --- > drivers/gpu/drm/drm_dp_mst_topology.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c > b/drivers/gpu/drm/drm_dp_mst_topology.c > index 7d2d31eaf003..a6473e3ab448 100644 > --- a/drivers/gpu/drm/drm_dp_mst_topology.c > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c > @@ -4707,6 +4707,9 @@ int drm_dp_mst_atomic_check_bw_limit(struct > drm_dp_mst_branch *branch, > struct drm_dp_vcpi_allocation *vcpi; > int pbn_limit = 0, pbn_used = 0; > > + if (!branch) > + return 0; > + > list_for_each_entry(port, &branch->ports, next) { > if (port->mstb) > if (drm_dp_mst_atomic_check_bw_limit(port->mstb, > mst_state)) -- Cheers, Lyude Paul