On Tue, Jul 14, 2026 at 4:47 AM Baineng Shou shoubaineng@gmail.com wrote:
fastrpc_ioctl_alloc_dmabuf() calls dma_buf_fd() which installs the fd into the caller's fd table before copy_to_user() copies the fd number back to userspace. If copy_to_user() fails, the fd is already visible to other threads in the same process but the ioctl returns -EFAULT. The existing comment in the code even acknowledges the problem:
"The usercopy failed, but we can't do much about it, as dma_buf_fd() already called fd_install()..."
Now that dma_buf_fd_install() is available (introduced to fix the same issue in dma-heap), apply the same pattern here: reserve the fd with get_unused_fd_flags(), attempt copy_to_user(), and only on success call dma_buf_fd_install() to publish it atomically with the tracepoint. On copy_to_user() failure, put_unused_fd() and dma_buf_put() cleanly unwind without any user-visible side effects.
Fixes: 6cffd79504ce ("misc: fastrpc: Add support for dmabuf exporter") Cc: stable@vger.kernel.org Signed-off-by: Baineng Shou shoubaineng@gmail.com
Reviewed-by: T.J. Mercier tjmercier@google.com