On 3/1/26 13:34, Julian Orth wrote:
> Consider the following application:
>
> #include <fcntl.h>
> #include <string.h>
> #include <drm/drm.h>
> #include <sys/ioctl.h>
>
> int main(void) {
> int fd = open("/dev/dri/renderD128", O_RDWR);
> struct drm_syncobj_create arg1;
> ioctl(fd, DRM_IOCTL_SYNCOBJ_CREATE, &arg1);
> struct drm_syncobj_handle arg2;
> memset(&arg2, 1, sizeof(arg2)); // simulate dirty stack
> arg2.handle = arg1.handle;
> arg2.flags = 0;
> arg2.fd = 0;
> arg2.pad = 0;
> // arg2.point = 0; // userspace is required to set point to 0
> ioctl(fd, DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD, &arg2);
> }
>
> The last ioctl returns EINVAL because args->point is not 0. However,
> userspace developed against older kernel versions is not aware of the
> new point field and might therefore not initialize it.
>
> The correct check would be
>
> if (args->flags & DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_TIMELINE)
> return -EINVAL;
>
> However, there might already be userspace that relies on this not
> returning an error as long as point == 0. Therefore use the more lenient
> check.
>
> Fixes: c2d3a7300695 ("drm/syncobj: Extend EXPORT_SYNC_FILE for timeline
> syncobjs")
> Signed-off-by: Julian Orth <[email protected]>
Good catch, Reviewed-by: Christian König <[email protected]>
As long as nobody objects I'm going to push this to drm-misc-fixes later today.
Thanks,
Christian.
> ---
> This patch fixes a regression that would cause conversions between
> syncobj handles and fds to fail if userspace did not initialize a
> recently-added field to 0.
> ---
> drivers/gpu/drm/drm_syncobj.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 250734dee928..49eccb43ce63 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -875,7 +875,7 @@ drm_syncobj_handle_to_fd_ioctl(struct drm_device *dev,
> void *data,
> return drm_syncobj_export_sync_file(file_private,
> args->handle,
> point, &args->fd);
>
> - if (args->point)
> + if (point)
> return -EINVAL;
>
> return drm_syncobj_handle_to_fd(file_private, args->handle,
> @@ -909,7 +909,7 @@ drm_syncobj_fd_to_handle_ioctl(struct drm_device *dev,
> void *data,
> args->handle,
> point);
>
> - if (args->point)
> + if (point)
> return -EINVAL;
>
> return drm_syncobj_fd_to_handle(file_private, args->fd,
>
> ---
> base-commit: eb71ab2bf72260054677e348498ba995a057c463
> change-id: 20260301-point-4305b6417f55
>
> Best regards,
> --
> Julian Orth <[email protected]>
>
