[PATCH] drm/syncobj: Fix handle <-> fd ioctls with dirty stack

[Julian Orth <ju.orth@gmail.com>]

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 <ju.orth@gmail.com>
---
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 <ju.orth@gmail.com>