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J . Mercier" , Benjamin Gaignard , Brian Starkey , John Stultz , Sandeep Patil , "Andrew F . Davis" , Srinivas Kandagatla 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 References: <20260714114654.3885457-1-shoubaineng@gmail.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20260714114654.3885457-1-shoubaineng@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MN0PR03CA0029.namprd03.prod.outlook.com (2603:10b6:208:52f::34) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|SN7PR12MB6742:EE_ X-MS-Office365-Filtering-Correlation-Id: 2a963880-8c1c-436d-2268-08dee1a2cf7c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; ARA:13230040|366016|23010399003|7416014|376014|1800799024|4143699003|18002099003|22082099003|11063799006|56012099006; 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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. drivers/gpu/drm/drm_prime.c is also using fd_install() of a DMA-buf file descriptor manually. Would be nice if we could us the new dma_buf_fd_install() for tracing here as well. Apart from that feel free to add Acked-by: Christian König to the whole series. Regards, Christian. > > 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/ > > Changes in v3: > - Split into two patches (dma-heap + fastrpc separately) > - Add dma_buf_fd_install() to preserve trace_dma_buf_fd tracepoint > (spotted by T.J. Mercier and sashiko-bot on v2) > - Add fastrpc fix using the new helper (suggested by T.J. Mercier) > > Baineng Shou (2): > dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds > misc: fastrpc: don't publish fd before copy_to_user() succeeds > > drivers/dma-buf/dma-buf.c | 20 ++++++++++ > drivers/dma-buf/dma-heap.c | 80 +++++++++++++++++++------------------- > drivers/misc/fastrpc.c | 16 +++----- > include/linux/dma-buf.h | 1 + > 4 files changed, 67 insertions(+), 50 deletions(-) >