[PATCH 5.4 100/108] drm: Return -ENOTTY for non-drm ioctls

Greg Kroah-Hartman
2021-07-26T16:15:29Z

From: Charles Baylis <cb-kernel@fishzet.co.uk>

commit 3abab27c322e0f2acf981595aa8040c9164dc9fb upstream.

drm: Return -ENOTTY for non-drm ioctls

Return -ENOTTY from drm_ioctl() when userspace passes in a cmd number
which doesn't relate to the drm subsystem.

Glibc uses the TCGETS ioctl to implement isatty(), and without this
change isatty() returns it incorrectly returns true for drm devices.

To test run this command:
$ if [ -t 0 ]; then echo is a tty; fi < /dev/dri/card0
which shows "is a tty" without this patch.

This may also modify memory which the userspace application is not
expecting.

Signed-off-by: Charles Baylis <cb-kernel@fishzet.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/YPG3IBlzaMhfPqCr@stando.fishzet.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/drm_ioctl.c | 3 +++
include/drm/drm_ioctl.h | 1 +
2 files changed, 4 insertions(+)

--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -826,6 +826,9 @@ long drm_ioctl(struct file *filp,
if (drm_dev_is_unplugged(dev))
return -ENODEV;

+ if (DRM_IOCTL_TYPE(cmd) != DRM_IOCTL_BASE)
+ return -ENOTTY;
+
is_driver_ioctl = nr >= DRM_COMMAND_BASE && nr < DRM_COMMAND_END;

if (is_driver_ioctl) {
--- a/include/drm/drm_ioctl.h
+++ b/include/drm/drm_ioctl.h
@@ -68,6 +68,7 @@ typedef int drm_ioctl_compat_t(struct fi
unsigned long arg);

#define DRM_IOCTL_NR(n) _IOC_NR(n)
+#define DRM_IOCTL_TYPE(n) _IOC_TYPE(n)
#define DRM_MAJOR 226

/**