From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Date: Sun, 27 Sep 2020 12:06:58 +0000 Subject: Re: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE Message-Id: <20200927120658.GA107433@kroah.com> List-Id: References: <000000000000226d3f05b02dd607@google.com> <47907f77-b14b-b433-45c6-a315193f0c1a@i-love.sakura.ne.jp> <494395bc-a7dd-fdb1-8196-a236a266ef54@i-love.sakura.ne.jp> <20200927092701.GA1037755@PWN> <4933b81b-9b1a-355b-df0e-9b31e8280ab9@i-love.sakura.ne.jp> In-Reply-To: <4933b81b-9b1a-355b-df0e-9b31e8280ab9@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tetsuo Handa Cc: syzbot , linux-fbdev@vger.kernel.org, George Kennedy , b.zolnierkie@samsung.com, daniel.vetter@ffwll.ch, deller@gmx.de, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Linus Torvalds , jirislaby@kernel.org, Peilin Ye On Sun, Sep 27, 2020 at 08:46:30PM +0900, Tetsuo Handa wrote: > syzbot is reporting UAF/OOB read at bit_putcs()/soft_cursor() [1][2], for > vt_resizex() from ioctl(VT_RESIZEX) allows setting font height larger than > actual font height calculated by con_font_set() from ioctl(PIO_FONT). > Since fbcon_set_font() from con_font_set() allocates minimal amount of > memory based on actual font height calculated by con_font_set(), > use of vt_resizex() can cause UAF/OOB read for font data. > > VT_RESIZEX was introduced in Linux 1.3.3, but it is unclear that what > comes to the "+ more" part, and I couldn't find a user of VT_RESIZEX. > > #define VT_RESIZE 0x5609 /* set kernel's idea of screensize */ > #define VT_RESIZEX 0x560A /* set kernel's idea of screensize + more */ > > So far we are not aware of syzbot reports caused by setting non-zero value > to v_vlin parameter. But given that it is possible that nobody is using > VT_RESIZEX, we can try removing support for v_clin and v_vlin parameters. Debian code search doesn't show any users, and that's usually a good indication of what userspace ioctls for old things like this, are being used for. So this makes sense to me, I'll queue it up, thanks! greg k-h