From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f171.google.com (mail-pg1-f171.google.com [209.85.215.171]) (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 29FE341A571 for ; Fri, 7 Aug 2026 10:09:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786097399; cv=none; b=DI9YAdR5/UbRZcLP08xEkrt9geJJ9zsow6xsehccGp3Cf+RLmbgP6XOdV1xstKgesbDymUWuHx/SKisbYj3x9zfiIbLtMYEeM+AXbKJl/VfObFKfCvJBL337K13IDItQbQcibF2sw3/PexXxYgVOeWckkBIc1UegA+g9Ujf2eoI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786097399; c=relaxed/simple; bh=Lh9CRmCJRCXUfNdf9uNGdR9iSpJFMr7nm3Cly0+0f/o=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=R2Yeb60iIkKzf6fdu7bSN+jDAoo7PGhWzSvkj8vzSNlY037SbWDva+LV4qU4TBbNaA8dcPB1mdI+K4iNZe9Y95BIfYriBXH/Qbikqj3/rYDj68UY70Iv857Ar4VZPJvG7cqME05uMUGyI3HlRPIlnYW76MJuTO3BhrjqB3ieoIs= 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=ryyqhbCN; arc=none smtp.client-ip=209.85.215.171 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="ryyqhbCN" Received: by mail-pg1-f171.google.com with SMTP id 41be03b00d2f7-c9e0b89e228so1917532a12.1 for ; Fri, 07 Aug 2026 03:09:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1786097397; x=1786702197; 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=ryyqhbCN27qKVoEeqMgJB9MEDkAxYHQbs1tB1JckFH+RUhT0jbEcJXxnnWBJp0h/go nAQi4W9aUTM+/hZ57vkLtykYA9Fl2915NYy4M/a4SWR0LImu6P5NvbIskt9q41glT18v chU2P7fr+LFVsYF9EuSmVHFVak0Nd/Zot8OSS69pS4DH3Nl0bMSPiGbdUhoD0wmVVRrt l5+47B0J3iTQG1ioDeplElR01abjCFCS/AHrBR6T5l+ViyUhCeFFIdQaG8o///fy2EH/ HcCO5PTkhZ6bmJkHSE++tq1jfjPCoDR/lg1W2cOSLZwW14ZpedQOzaB0lWJG/kI256m8 Sw/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786097397; x=1786702197; 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=fnn0IPYI/IcU3kWOjnqbwVVtJUqq8uHv2HCbr/HLsT8N2aNTzjzicKUgjn7mbPZn2u hCJGpI/TWLRIhxLZowhJzr2Xl7H/3x2ZjSs/eZrkeYwIRYz/RrupG+qBq84ir1uMWEfy bwDBlMiD6byxzT7/mmEghnnB1ibCg6uWlsmSAz0o3XIyZMyiMgikcrrwitlrL+OKNyJ/ iBeVdITGgz7p3gZ1RiMsF+dGS1yKYgzCGuBmuKc/Uk4IqFgHIAAKW9TnFlTp8xOV/SuB 2DQ2vgsrJf2eERO02hEiXrdqb3sVKoghLxVM2kyHLtkeQARgtD9TcBqWfGdp18brUzSf 1tcQ== X-Forwarded-Encrypted: i=1; AHgh+RqVERDKnuelTWwBkekFZdw1VC/5kZQAepmSiMrWaVSPqO3vM2IHXtPMOWFdEVTo85Z59e3nRQq4w+e6ZNE=@vger.kernel.org X-Gm-Message-State: AOJu0YwO2p25y/2h5dTfG6VvnQG6UIIs3dYBYA9XYhICWSdqZNZKk/4l Fqz6s1XfORRSsb7rZHTiK3tO9lWLwC5aMkBP0MwLwh7dCZGd4SDCcqqY X-Gm-Gg: AR+sD11adzHiqfCLoMQD0MQCfKuTxq1r8TghRcZTWermuBjUfYCBkaiIpBcAXBAIOyc PckQh5nEUjW9G/9JL0S+XgPeDIvF1KftrX/Ovsw3wCShZlDOYK8lm0LAD4zF+KyvoMuCCmSE8Bp Wvrh+1/KzbkEUDe2Sy33it5dWxpPvFvXTfpqIrR60bQNBzV9sibI677Bv0EALOnrzn2z52EY2zx psOAz+J71HsNlksIYQEBKwyLLsk51nZumjZkjiTGyVZ/j3OJ1bFH9myL8cKk0tFtCLzYzm0oARZ yHkLV3Nb84U2a7Yy6vBSGuotKRrmJMW/BYgwKpwROgxMHxGp6sxauzA5dySW84dMsctLDh0zA7c xemx/521N5VSTGRyp9PlRNdWsIDyq9JXcQOXbJruksFUZS6ARdpxAhKKlTJ4oZAv5pQiq3w70tN Jql60YXmEV9qpM/2w9qVuCBhF3WTR9mc5y/uUDD/xpT7WL6AK6mFnrnmUj/EOCUtOHvWB9BTDfe 2Q= X-Received: by 2002:a17:90b:224e:b0:38e:9ef9:eb97 with SMTP id 98e67ed59e1d1-3903c5c443dmr18527888a91.16.1786097397142; Fri, 07 Aug 2026 03:09:57 -0700 (PDT) Received: from baineng-pc.. ([117.133.183.252]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39085de8ddcsm4363444a91.6.2026.08.07.03.09.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Aug 2026 03:09:56 -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 18:09:37 +0800 Message-Id: <20260807100941.1351356-1-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