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 --- drivers/misc/fastrpc.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c index f3a49384586d..c5143cd25767 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -1709,24 +1709,20 @@ static int fastrpc_dmabuf_alloc(struct fastrpc_user *fl, char __user *argp) return err; }
- bp.fd = dma_buf_fd(buf->dmabuf, O_ACCMODE); + bp.fd = get_unused_fd_flags(O_ACCMODE); if (bp.fd < 0) { dma_buf_put(buf->dmabuf); - return -EINVAL; + return bp.fd; }
if (copy_to_user(argp, &bp, sizeof(bp))) { - /* - * 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 It - * might already be closed and dmabuf no longer valid when - * we reach this point.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. - */ + put_unused_fd(bp.fd); + dma_buf_put(buf->dmabuf); return -EFAULT; }
+ dma_buf_fd_install(buf->dmabuf, bp.fd); + return 0; }