From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0F2223F328F for ; Fri, 7 Aug 2026 10:10:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786097419; cv=none; b=ZqvigfTpbHursYhfQ5q3d5m5Ns1VTUQyNkoshXwdd33DEJjX66Lfq4v2aS0kLzT/0ck2sj3Rn++gvDdcTaYNKYg2oYUBGJ5qf/2rksfNP4FvqisWeh9l7jB079sCF9wQocviMiWLWtBgvvP3n/7LWad2KZo2zerbyBOlG3ZfFHk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786097419; c=relaxed/simple; bh=Lh9CRmCJRCXUfNdf9uNGdR9iSpJFMr7nm3Cly0+0f/o=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=DNUkf2dtI/rhSKwBqz89L17Gp4ncBMBoDTOgqOSljimQGs4IDsGkmt8nfsnFRh7duPtVrcHENgCqhh+wbZU76AstZTTmNqwFzBJk0SxAcl9GaX4T96yfAmPMSeRVviqzn+A5Cgg2waHSHWQl6IWp04J3osCXOwJyiQLdqzS/7+4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=eDStJmLx; arc=none smtp.client-ip=209.85.210.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="eDStJmLx" Received: by mail-pf1-f182.google.com with SMTP id d2e1a72fcca58-8485ef63b68so4725805b3a.1 for ; Fri, 07 Aug 2026 03:10:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1786097417; x=1786702217; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=MQciLaflxhQrAIWokNvSZ9sUyM0S9LcjwfcEZLUvgpA=; b=eDStJmLx9l7r1NTCiXWzauCpJHG+HacCUCkPA2AC6N5px2RlHgG3js0PJaySKKviuP SFigkp287QwKLZCuYN7XITo77OYCaB+xq1zbLQpET022/EZwXl0izjn8qs/izEh7bqmq qi5AStkzgv6efA5wX8YRJJLo0k/ehMOsk62FoLdVtHZTUewkGl5yxKL7Uurm50LXg6IT /NSpNSm65aDPwhkojT9kdctoJGqkmT2a+5GKJd9GuG5Bm4PjcTIIeiPOms2hUeNlBOsm 9NzWXrxJ3Gd/SMBbHVq9cJlrCP5FzPyyPMaC360N56arGopuJzPLSnmrxoXqkfSTK83Q +zQg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786097417; x=1786702217; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=MQciLaflxhQrAIWokNvSZ9sUyM0S9LcjwfcEZLUvgpA=; b=LePtOI+JdN7zDW5rwC1NkKMEzBljqdi190F/IGc6UPVq7E+sH+j5OFGnpyKcePLX3F wuKNyF9vOv24og6mxRFbosifSt5rcOJcy0psr8pOgiR7wFnJJ5/BQ2+o1zq91HT1Sijs vMm+wDIkB2IFopTjpF/YuuV/ZzNhMB6e/thAiF3P5+jf2B8G80DC0G5SUS3s9pf6OJ5m v4DHwr7DShbhRPR+iTXou8aTEK39+aXsN2w7MnF2dn/YFpsVUCx8XFAuMnovIhZNyEJE boAjAThjfZFdTDsRlFssWXUkUzlomqYaH0ad+xW/0fOT2Bd5WLT7ALF8VKBXum1+jDKn Et2A== X-Forwarded-Encrypted: i=1; AHgh+RrP+Oj85fRCB9rA7m/VJaa8aBYlGsbtYcJGTcwh5Hk+l50ef19dWHliLgjyLpQu47ShjC1Oq0EzSRU2TwU=@vger.kernel.org X-Gm-Message-State: AOJu0YxWWiQtNOselxcibn5NcNEhwoMbxqdiK/+TxMIfTqTjgh69Vhb2 WGsK8IsAV+3nHY5pcHh3UWMtlYqLxrTfuIUFFNdQPTlmRw4a+1Y3sWLq X-Gm-Gg: AR+sD10jlUbze//BYxaOZnvBDHxmOtR6TUa6pekVZ5umlCO5+Zc8TTO1jXqjzAYGXsO sAgJu2rH9DfadgUafYVaQhzW5tZ85x+ZuUKGvzJHlLi9KxjcAMnDQXC4fmIKe0WB5eDKFnF/ZAt ImXn9tX6EZ2E08HTPhE5oQS18n/R0BmCttetdqL/pwtKxfdYibHFP5uneg0H+IQe+jrDKcgQ9cy H1CC0lrALGYen84ji2/dgsD642lz8Uj9/mVNRQDdrCl+y3M6PCSoiBrjJ7ayb2fBrYddMU5TI7g Y2NG+xv9FAcfThv4pYIMT8khkx/0XNgcRdli2ehabZlDdRyKDYmoBMBSmgGhFViIAshEqg5IPUl OrZ+yjxs4XvZDG0rLp+uiR5NdsCOQkjXsrtPFz6uIX9jP7Z8p3Pdu6bixpn9kFnf5XKdEx+qQtk ubwlX6WirvtuA5/NpT4a51maxg2NVxO+/DbCqb7ynfdmhriJN0VgUGZpu8JfQN3KRA X-Received: by 2002:a05:6a00:2d0c:b0:84e:2382:f4f0 with SMTP id d2e1a72fcca58-84f2dfc8ed4mr23153657b3a.4.1786097417043; Fri, 07 Aug 2026 03:10:17 -0700 (PDT) Received: from baineng-pc.. ([117.133.183.252]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84f5a5528adsm795291b3a.45.2026.08.07.03.10.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2026 03:10:16 -0700 (PDT) From: Baineng Shou To: Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , "T . J . Mercier" , Benjamin Gaignard , Brian Starkey , John Stultz , Sandeep Patil , "Andrew F . Davis" , Srinivas Kandagatla , David Airlie , Simona Vetter Cc: stable@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Baineng Shou Subject: [PATCH v6 0/4] dma-buf: fix fd leak when copy_to_user() fails after fd_install() Date: Fri, 7 Aug 2026 18:10:02 +0800 Message-Id: <20260807101006.1352561-1-shoubaineng@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: 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: 8bit Several drivers call dma_buf_fd() — which internally calls fd_install() — before copy_to_user() returns the fd number to userspace. If copy_to_user() fails, the fd is already published in the caller's fd table but the ioctl returns an error, so userspace never learns the fd number. Worse, the window between fd_install() and copy_to_user() allows other threads to observe and manipulate the fd (dup, close, SCM_RIGHTS), making any "close it on the failure path" fix unsafe. The fix is to split the allocation into three steps: reserve an fd with get_unused_fd_flags() (not yet visible to other threads), do copy_to_user(), and only then publish the fd with fd_install() via the new dma_buf_fd_install() helper. On copy_to_user() failure, put_unused_fd() + dma_buf_put() cleanly unwind with no user-visible side effects. Patch 1 introduces dma_buf_fd_install() in dma-buf.c (wrapping fd_install() together with the DMA_BUF_TRACE call to preserve export tracing) and applies the fix to dma-heap. Patch 2 applies the same fix to fastrpc, which even had a comment acknowledging the problem could not be fixed before. Patch 3 replaces the bare fd_install() in drm_gem_prime_handle_to_fd() with dma_buf_fd_install() to restore tracepoint coverage for DRM PRIME exports (suggested by Christian König). Patch 4 adds a selftest to tools/testing/selftests/dmabuf-heaps/ that reproduces the fd-leak scenario (mprotect flip before the ioctl) and verifies the fd count is unchanged after a failed ioctl (suggested by Sumit Semwal). v1: https://lore.kernel.org/dri-devel/20260703080922.1838362-1-shoubaineng@gmail.com/ v2: https://lore.kernel.org/dri-devel/20260710105430.3059661-1-shoubaineng@gmail.com/ v3: https://lore.kernel.org/dri-devel/20260714114654.3885457-1-shoubaineng@gmail.com/ Changes in v6: - Rework the selftest (patch 4) per review: extract a count_open_fds() helper, fix the copy_from_user() comment, fail (not skip) when the ioctl does not return -1, drop the bogus mprotect-race mention, and reword the result message. Changes in v5: - Add selftest (patch 4) reproducing the fd-leak scenario (Sumit Semwal) Changes in v4: - Add patch 3: drm/prime: use dma_buf_fd_install() (Christian König) - Add Acked-by: Christian König to patches 1 and 2 Changes in v3: - Split into two patches (dma-heap + fastrpc separately) - Add dma_buf_fd_install() to preserve trace_dma_buf_fd tracepoint - Add fastrpc fix using the new helper (T.J. Mercier) Baineng Shou (4): dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds misc: fastrpc: don't publish fd before copy_to_user() succeeds drm/prime: use dma_buf_fd_install() to preserve export tracing selftests: dmabuf-heaps: add fd-leak-on-EFAULT regression test drivers/dma-buf/dma-buf.c | 20 ++++ drivers/dma-buf/dma-heap.c | 80 ++++++------- drivers/gpu/drm/drm_prime.c | 2 +- drivers/misc/fastrpc.c | 16 +-- include/linux/dma-buf.h | 1 + .../selftests/dmabuf-heaps/dmabuf-heap.c | 113 +++++++++++++++++- 6 files changed, 180 insertions(+), 52 deletions(-) -- 2.34.1