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[212.51.149.33]) by smtp.gmail.com with ESMTPSA id c14-20020a5d4cce000000b002f2782978d8sm4178312wrt.20.2023.04.11.06.44.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Apr 2023 06:44:44 -0700 (PDT) Date: Tue, 11 Apr 2023 15:44:41 +0200 From: Daniel Vetter To: Intel Graphics Development Cc: Daniel Vetter , Daniel Vetter , Alex Deucher , shlomo@fastmail.com, Michel =?iso-8859-1?Q?D=E4nzer?= , Noralf =?iso-8859-1?Q?Tr=F8nnes?= , Thomas Zimmermann , Maarten Lankhorst , Maxime Ripard , David Airlie , Daniel Vetter , dri-devel@lists.freedesktop.org, stable@vger.kernel.org, Bartlomiej Zolnierkiewicz , Geert Uytterhoeven , Nathan Chancellor , Qiujun Huang , Peter Rosin , linux-fbdev@vger.kernel.org, Helge Deller , Sam Ravnborg , Geert Uytterhoeven , Samuel Thibault , Tetsuo Handa , Shigeru Yoshida Subject: Re: [PATCH] fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace Message-ID: References: <20230404193934.472457-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230404193934.472457-1-daniel.vetter@ffwll.ch> X-Operating-System: Linux phenom 6.1.0-7-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org On Tue, Apr 04, 2023 at 09:39:34PM +0200, Daniel Vetter wrote: > 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 > Fixes: dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore") > Cc: Alex Deucher > Cc: shlomo@fastmail.com > Cc: Michel Dänzer > Cc: Noralf Trønnes > Cc: Thomas Zimmermann > Cc: Daniel Vetter > Cc: Maarten Lankhorst > Cc: Maxime Ripard > Cc: David Airlie > Cc: Daniel Vetter > Cc: dri-devel@lists.freedesktop.org > Cc: # v5.7+ > Cc: Bartlomiej Zolnierkiewicz > Cc: Geert Uytterhoeven > Cc: Nathan Chancellor > Cc: Qiujun Huang > Cc: Peter Rosin > Cc: linux-fbdev@vger.kernel.org > Cc: Helge Deller > Cc: Sam Ravnborg > Cc: Geert Uytterhoeven > Cc: Samuel Thibault > Cc: Tetsuo Handa > Cc: Shigeru Yoshida An Ack on this (or a better idea) would be great, so I can stuff it into -fixes. Thanks, Daniel > --- > 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 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch