This is a note to let you know that I've just added the patch titled misc: fastrpc: avoid double fput() on failed usercopy to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: misc-fastrpc-avoid-double-fput-on-failed-usercopy.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit f8174217e083399a26978975e7e63e6e77f058c6 Author: Mathias Krause <minipli@xxxxxxxxxxxxxx> Date: Thu Jan 27 14:02:18 2022 +0100 misc: fastrpc: avoid double fput() on failed usercopy [ Upstream commit 46963e2e0629cb31c96b1d47ddd89dc3d8990b34 ] If the copy back to userland fails for the FASTRPC_IOCTL_ALLOC_DMA_BUFF ioctl(), we shouldn't assume that 'buf->dmabuf' is still valid. In fact, dma_buf_fd() called fd_install() before, i.e. "consumed" one reference, leaving us with none. Calling dma_buf_put() will therefore put a reference we no longer own, leading to a valid file descritor table entry for an already released 'file' object which is a straight use-after-free. Simply avoid calling dma_buf_put() and rely on the process exit code to do the necessary cleanup, if needed, i.e. if the file descriptor is still valid. Fixes: 6cffd79504ce ("misc: fastrpc: Add support for dmabuf exporter") Acked-by: Christian König <christian.koenig@xxxxxxx> Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220127130218.809261-1-minipli@xxxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c index ef49ac8d91019..d0471fec37fbb 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -1284,7 +1284,14 @@ static int fastrpc_dmabuf_alloc(struct fastrpc_user *fl, char __user *argp) } if (copy_to_user(argp, &bp, sizeof(bp))) { - dma_buf_put(buf->dmabuf); + /* + * The usercopy failed, but we can't do much about it, as + * dma_buf_fd() already called fd_install() and made the + * file descriptor accessible for the current process. It + * might already be closed and dmabuf no longer valid when + * we reach this point. Therefore "leak" the fd and rely on + * the process exit path to do any required cleanup. + */ return -EFAULT; }