[Intel-gfx] [PATCH] fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace

* [Intel-gfx] [PATCH] fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace
@ 2023-04-04 19:39 Daniel Vetter
  2023-04-04 22:10 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for " Patchwork
                   ` (4 more replies)
  0 siblings, 5 replies; 9+ messages in thread
From: Daniel Vetter @ 2023-04-04 19:39 UTC (permalink / raw)
  To: Intel Graphics Development
  Cc: linux-fbdev, Shigeru Yoshida, Geert Uytterhoeven, David Airlie,
	Daniel Vetter, dri-devel, Daniel Vetter, Sam Ravnborg,
	Helge Deller, Tetsuo Handa, Geert Uytterhoeven, Samuel Thibault,
	Thomas Zimmermann, Bartlomiej Zolnierkiewicz, Michel Dänzer,
	Maxime Ripard, shlomo, Nathan Chancellor, stable,
	Noralf Trønnes, Daniel Vetter, Alex Deucher, Peter Rosin,
	Qiujun Huang

This is an oversight from dc5bdb68b5b3 ("drm/fb-helper: Fix vt
restore") - I failed to realize that nasty userspace could set this.

It's not pretty to mix up kernel-internal and userspace uapi flags
like this, but since the entire fb_var_screeninfo structure is uapi
we'd need to either add a new parameter to the ->fb_set_par callback
and fb_set_par() function, which has a _lot_ of users. Or some other
fairly ugly side-channel int fb_info. Neither is a pretty prospect.

Instead just correct the issue at hand by filtering out this
kernel-internal flag in the ioctl handling code.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Fixes: dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore")
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: shlomo@fastmail.com
Cc: Michel Dänzer <michel@daenzer.net>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.7+
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Qiujun Huang <hqjagain@gmail.com>
Cc: Peter Rosin <peda@axentia.se>
Cc: linux-fbdev@vger.kernel.org
Cc: Helge Deller <deller@gmx.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Shigeru Yoshida <syoshida@redhat.com>
---
 drivers/video/fbdev/core/fbmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 875541ff185b..3fd95a79e4c3 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1116,6 +1116,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 	case FBIOPUT_VSCREENINFO:
 		if (copy_from_user(&var, argp, sizeof(var)))
 			return -EFAULT;
+		/* only for kernel-internal use */
+		var.activate &= ~FB_ACTIVATE_KD_TEXT;
 		console_lock();
 		lock_fb_info(info);
 		ret = fbcon_modechange_possible(info, &var);
-- 
2.40.0


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