From nobody Fri Dec 19 07:20:06 2025 Received: from smtpout-04.galae.net (smtpout-04.galae.net [185.171.202.116]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D59EB2D9EFC; Tue, 16 Dec 2025 18:00:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.171.202.116 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765908002; cv=none; b=MCr2AJT0V1M2BqwOoWuuzKnj9DWOMouRKq4TBV3gMLngIaWlr/Fma1jt97+F9eibkGwfztKVkigH7OWMCyVD0hn7uwUv4HnFxg0Z4k06rjrTiDjSRwK0971HW6nlSXXK5cwtwzaRtjfqdrjqA1kFr0pD4S75IjjJN/AXEt8INVc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765908002; c=relaxed/simple; bh=emDhk2MMrd8ZT9IWg/kP2hcjE9Z97TjWHRlexkv8XLo=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=FwD13QEKnuMXaOK0k/Fn2yny6CS81Gx5wUxG9mEJbzkf6ehH0QC1Xhg0yaQ1K7ZkF+YKLI5RYKWUnGYwW0eQ/S06+rpudsbCHq90bXCnvRD2NugAEX9/080HPbyNckrwV7CWM1gErmFKqz1iBkEoZat+FV0sJI2qiB/EYTN+2zQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=rlEm/gAv; arc=none smtp.client-ip=185.171.202.116 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="rlEm/gAv" Received: from smtpout-01.galae.net (unknown [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id A2637C1A582; Tue, 16 Dec 2025 17:59:34 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 1B9576071C; Tue, 16 Dec 2025 17:59:49 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 38D9A119A97D5; Tue, 16 Dec 2025 18:59:44 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1765907987; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=GmMyYFYj3nN0WWZncwkj3rSY84I1KnZQTlsrUpqIOyA=; b=rlEm/gAvrMbqr3Pj4NGgu9O+LbFKm4iDqhBczJ0MFSNJklRloeIRAsDfvYUSxHPtjJWmFM 6cKCOdkflGuz5f+0Xzgl4l41lVU9rNcFeNpED8pEwgaK5E1Dh0Rx6A+hmEkY7o2ER5tac2 iLb7R0CH6J9upYVCg2ct4zQpvQ4DLr1Uu61thZsTh+NsXqpghIXzsPTWE58VzrBsT7RY8m zIbD39BzKVIUskMhJL9ZTmLtiEw1VU1Qae5G5aHZzgeHureeVPrrjAa0hhcNsCXOD4kS4Z thOY1qJd+CovZN8O/Go0lIxNieqk/vbiHGq4dK2f2WiTYpmeMRfXc52pPvzQCA== From: Luca Ceresoli Date: Tue, 16 Dec 2025 18:58:39 +0100 Subject: [PATCH v3 06/22] drm/bridge: add next_bridge pointer to struct drm_bridge Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-6-b5165fab8058@bootlin.com> References: <20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-0-b5165fab8058@bootlin.com> In-Reply-To: <20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-0-b5165fab8058@bootlin.com> To: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jonathan Corbet , Alexey Brodkin , Phong LE , Liu Ying , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Kevin Hilman , Jerome Brunet , Martin Blumenstingl Cc: Hui Pu , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, Luca Ceresoli X-Mailer: b4 0.14.3 X-Last-TLS-Session-Version: TLSv1.3 Many bridge drivers store a next_bridge pointer in their private data and use it for attach and sometimes other purposes. This is going to be risky when bridge hot-unplug is used. Considering this example scenario: 1. pipeline: encoder --> bridge A --> bridge B --> bridge C 2. encoder takes a reference to bridge B 3. bridge B takes a next_bridge reference to bridge C 4. encoder calls (bridge B)->b_foo(), which in turns references next_bridge, e.g.: b_foo() { bar(b->next_bridge); } If bridges B and C are removed, bridge C can be freed but B is still allocated because the encoder holds a reference to B. So when step 4 happens, 'b->next-bridge' would be a use-after-free. Calling drm_bridge_put() in the B bridge .remove function does not solve the problem as it leaves a (potentially long) risk window between B removal and the final deallocation of B. A safe moment to put the B reference is in __drm_bridge_free(), when the last reference has been put. This can be done by drivers in the .destroy func. However to avoid the need for so many drivers to implement a .destroy func, just offer a next_bridge pointer to all bridges that is automatically put it in __drm_bridge_free(), exactly when the .destroy func is called. Suggested-by: Maxime Ripard Link: https://lore.kernel.org/all/20251201-thick-jasmine-oarfish-1eceb0@hou= at/ Signed-off-by: Luca Ceresoli Reviewed-by: Maxime Ripard --- drivers/gpu/drm/drm_bridge.c | 2 ++ include/drm/drm_bridge.h | 11 +++++++++++ 2 files changed, 13 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 64aa69dcf46f..6dcf8f6d3ecf 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -275,6 +275,8 @@ static void __drm_bridge_free(struct kref *kref) if (bridge->funcs->destroy) bridge->funcs->destroy(bridge); =20 + drm_bridge_put(bridge->next_bridge); + kfree(bridge->container); } =20 diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h index 8f10d2fd6016..63660256c4f5 100644 --- a/include/drm/drm_bridge.h +++ b/include/drm/drm_bridge.h @@ -1278,6 +1278,17 @@ struct drm_bridge { * @hpd_cb. */ void *hpd_data; + + /** + * @next_bridge: Pointer to the following bridge, automatically put + * when this bridge is freed (i.e. at destroy time). This is for + * drivers needing to store a pointer to the next bridge in the + * chain, and ensures any code still holding a reference to this + * bridge after its removal cannot use-after-free the next + * bridge. Any other bridge pointers stored by the driver must be + * put in the .destroy callback by driver code. + */ + struct drm_bridge *next_bridge; }; =20 static inline struct drm_bridge * --=20 2.52.0