Revert "drm/nouveau: check ioctl command codes better"

My previous patch ended up causing a regression for the
DRM_IOCTL_NOUVEAU_NVIF ioctl. The intention of my patch was to only
pass ioctl commands that have the correct dir/type/nr bits into the
nouveau_abi16_ioctl() function.

This turned out to be too strict, as userspace does use at least
write-only and write-read direction settings. Checking for both of these
still did not fix the issue, so the best we can do for the 6.16 release
is to revert back to what we've had since linux-3.16.

This version is still fragile, but at least it is known to work with
existing userspace. Fixing this properly requires a better understanding
of what commands are being passed from userspace in practice, and how
that relies on the undocumented (miss)behavior in nouveau_drm_ioctl().

Fixes: e547816 ("drm/nouveau: check ioctl command codes better")
Reported-by: Satadru Pramanik <[email protected]>
Closes: https://lore.kernel.org/lkml/CAFrh3J85tsZRpOHQtKgNHUVnn=EG=QKBnZTRtWS8eWSc1K1xkA@mail.gmail.com/
Reported-by: Chris Bainbridge <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Arnd Bergmann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Add Closes: tags, fix minor typo in commit message. - Danilo ]
Signed-off-by: Danilo Krummrich <[email protected]>

Author: arndb

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -1284,9 +1284,6 @@ nouveau_ioctls[] = {
 	DRM_IOCTL_DEF_DRV(NOUVEAU_EXEC, nouveau_exec_ioctl_exec, DRM_RENDER_ALLOW),
 };
 
-#define DRM_IOCTL_NOUVEAU_NVIF _IOC(_IOC_READ | _IOC_WRITE, DRM_IOCTL_BASE, \
-				    DRM_COMMAND_BASE + DRM_NOUVEAU_NVIF, 0)
-
 long
 nouveau_drm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
@@ -1300,10 +1297,14 @@ nouveau_drm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return ret;
 	}
 
-	if ((cmd & ~IOCSIZE_MASK) == DRM_IOCTL_NOUVEAU_NVIF)
+	switch (_IOC_NR(cmd) - DRM_COMMAND_BASE) {
+	case DRM_NOUVEAU_NVIF:
 		ret = nouveau_abi16_ioctl(filp, (void __user *)arg, _IOC_SIZE(cmd));
-	else
+		break;
+	default:
 		ret = drm_ioctl(file, cmd, arg);
+		break;
+	}
 
 	pm_runtime_mark_last_busy(dev->dev);
 	pm_runtime_put_autosuspend(dev->dev);