From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794590187; b=jz8Fp+6ZSjfxaUgOgnB4xO1fDj+D2pCwMFQHWim7qUj+IRxt84XzJtv5s5Hj0BXLkwex TUfQrnKC7ZBrnSgXyyc6hb/mglenVSOu18yuhMcdLB00HTc9LTkXO+yit7J4oemg5CodF SPBcdTKUgMMlhy+9iCx7iIrdfdj40jhOjiGOE4RolF1/9IydGRGIjh8NMS26bwJpJ2Nhv KWK3kRtxTYaytvA4Zog32lJp1bjdLZW1/m5Xi2y/Z0cAlXDu0w/7tPaN5//0OYHQCWTeV XbP0G3WY6Tztyl1Fm/6BkR6wipYcFi4YhdELRGTKfquPzoIrJcWcyCuLySJCbgqJrjA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590187; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=nrA87SNNUUOOEU8GI2yeCc35KlTRLe1I5bq7JjXPIr0=; b=0pAIytSExFT1narwJeddy0Th7yedYGg7DzfoD6rkEzTIdNECVs9Rxy02dk2itCqAnvkP biRQAOtzCheULDBnBXL7vJnPrXIgb+6slvoqtXe6CnoEy7u40Q8+6mwINSozx5hCLivP/ CAie0Gyx1wFkNSKDde+iX24uO6C+T+3cMiKMtgeequTcuhJ4goz8H12Hw5YZyfO6aNIqx hQaC85q4u8fffLU1FZByNaIwzBYw30A549DNU5XZBDda3018DdCcsRYu8DDLauxHcICv3 rWxaZxvvjgQP2FyQUyVZch5SwBzIm4m3hHAkbH7ipY/ZEVhTTr1eWuyRHsNh/ZLtfBg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=GERZK0x9; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 857B26073207; Fri, 13 Nov 2026 17:16:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=GERZK0x9 Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6FFC1F000C4; Fri, 13 Nov 2026 17:16:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590187; bh=nrA87SNNUUOOEU8GI2yeCc35KlTRLe1I5bq7JjXPIr0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GERZK0x9x6s+gxxia181vigOPxjAH6yNx3AVx+KasDmKsxC2pWJ0ayoFRjVw1uMye saBcB8byAWOyAVBRFfb87SwaCsGgvUinELb05orhFp8is1GxDTqIVOwtZz3w+0ojOH DAwpXhR5VIyAqsCgPjofpoXUAnDs/BNDF1AlPSh8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Andr=C3=A9=20Draszik?= , Philipp Stanner , =?UTF-8?q?Christian=20K=C3=B6nig?= , Sasha Levin Subject: [PATCH 6.18 196/686] drm/drm_crtc: ensure dma_fence_ops remain valid during device unbind Date: Fri, 13 Nov 2026 10:45:29 -0500 Message-ID: <20261113153827.681503824@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: André Draszik [ Upstream commit 3be436cbd3d265fe4fcfbb5b650edad7b2108443 ] In [1], sashiko reported the following issue: === snip === Looking at how these fences are managed, drm_crtc_create_fence() creates a dma_fence without taking a reference to the drm_device or drm_crtc. Because the sync_file framework exposes this fence to userspace, the fence can outlive the CRTC. The dma_fence contract requires that data accessed by dma_fence_ops (like get_driver_name) must remain valid for an RCU grace period after the fence is signaled. However, drm_crtc_cleanup() and the subsequent freeing of the device do not wait for an RCU grace period via synchronize_rcu(). If userspace calls ioctl(SYNC_IOC_FILE_INFO) concurrently with a device hot-unplug: CPU1 (Userspace) sync_file_get_name() ops = rcu_dereference(fence->ops); if (!dma_fence_test_signaled_flag()) // Preempted or delayed here CPU2 (Driver Teardown) Signals the fence (setting fence->ops = NULL) Destroys and frees the CRTC without waiting for an RCU grace period CPU1 (Resumes) ops->get_driver_name(fence) -> drm_crtc_fence_get_driver_name() crtc = fence_to_crtc(fence); // Casts to the freed CRTC return crtc->dev->driver->name; // Use-after-free ... Does the CRTC or DRM device need to be kept alive for the RCU grace period, or should the fence hold a proper reference to prevent the use-after-free when get_driver_name() and get_timeline_name() access the freed CRTC structure? === snap === I believe this to be a correct observation and this patch implements the suggestion of waiting for an RCU grace period before proceeding with destruction of the drm_crtc, so that get_driver_name() and get_timeline_name() can still work. Link: https://sashiko.dev/#/patchset/20260618-linux-drm_crtc_fix2-v1-1-c03e77b36f34@linaro.org?part=1 Fixes: 6d6003c4b613 ("drm/fence: add fence timeline to drm_crtc") Cc: stable@vger.kernel.org Signed-off-by: André Draszik Reviewed-by: Philipp Stanner Reviewed-by: Christian König Link: https://lore.kernel.org/r/20260721-linux-drm_crtc_fix2-v3-1-afa8c71506e6@linaro.org Signed-off-by: Christian König Signed-off-by: Sasha Levin --- drivers/gpu/drm/drm_crtc.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c index 46655339003db..4ba190287c2ac 100644 --- a/drivers/gpu/drm/drm_crtc.c +++ b/drivers/gpu/drm/drm_crtc.c @@ -476,14 +476,23 @@ EXPORT_SYMBOL(__drmm_crtc_alloc_with_planes); * drm_crtc_cleanup - Clean up the core crtc usage * @crtc: CRTC to cleanup * - * This function cleans up @crtc and removes it from the DRM mode setting - * core. Note that the function does *not* free the crtc structure itself, - * this is the responsibility of the caller. + * This function cleans up @crtc and removes it from the DRM mode setting core, + * after first waiting an RCU grace period to ensure @crtc->dev can safely be + * dereferenced by our dma_fence_ops. + * + * Note that the function does *not* free the crtc structure itself, this is the + * responsibility of the caller. */ void drm_crtc_cleanup(struct drm_crtc *crtc) { struct drm_device *dev = crtc->dev; + /* Ensure our dma_fence_ops remain valid for an RCU grace period after + * the fence is signaled. This is necessary because our dma_fence_ops + * dereference crtc->dev. + */ + synchronize_rcu(); + /* Note that the crtc_list is considered to be static; should we * remove the drm_crtc at runtime we would have to decrement all * the indices on the drm_crtc after us in the crtc_list. -- 2.53.0