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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	"Maciej W. Rozycki" <macro@orcam.me.uk>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
	Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Colin King <colin.king@canonical.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jani Nikula <jani.nikula@intel.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	"Antonino A. Daplas" <adaplas@gmail.com>
Subject: [PATCH v2] tty: vt: always invoke vc->vc_sw->con_resize callback
Date: Sat, 15 May 2021 16:43:49 +0900	[thread overview]
Message-ID: <97f1d292-c3a8-f4d6-0651-b4f5571ecb72@i-love.sakura.ne.jp> (raw)
In-Reply-To: <CAHk-=wjkVAjfWrmmJnJe1_MriK9gezWCew_MU=MbQNzHbGopsQ@mail.gmail.com>

On 2021/05/15 1:19, Tetsuo Handa wrote:
> Even if it turns out to be safe to always call this
> callback, we will need to involve another callback via "struct fb_ops" for
> checking the upper limits from fbcon_resize(). As a result, we will need
> to modify
> 
>  drivers/tty/vt/vt.c
>  drivers/video/fbdev/core/fbcon.c
>  drivers/video/fbdev/vga16fb.c
>  include/linux/fb.h
> 
> files only for checking rows/columns values passed to ioctl(VT_RESIZE)
> request.

I was by error assuming that fbcon_resize() cannot reject bogus rows/columns
and thus we need to add another callback via "struct fb_ops" for that purpose.
But fbcon_resize() does reject bogus rows/columns; it was simply because
resize_screen() did not call fbcon_resize() if vc->vc_mode == KD_GRAPHICS.
Thus, removing vc->vc_mode check alone is sufficient.

On 2021/05/15 6:10, Linus Torvalds wrote:
> So I think just removing the "vc->vc_mode != KD_GRAPHICS" test from
> resize_screen() might be the way to go. That way, the low-level data
> structures actually are in sync with the resize, and the "out of
> bounds" bug should never happen.
> 
> Would you mind testing that?

OK. Your suggested changes passed the test by me and by syzbot.



From e5e326c90c5b919c6aba30072d665a00b18715a5 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 15 May 2021 03:00:37 +0000
Subject: [PATCH v2] tty: vt: always invoke vc->vc_sw->con_resize callback

syzbot is reporting OOB write at vga16fb_imageblit() [1], for
resize_screen() from ioctl(VT_RESIZE) returns 0 without checking whether
requested rows/columns fit the amount of memory reserved for the graphical
screen if current mode is KD_GRAPHICS.

----------
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/kd.h>
#include <linux/vt.h>

int main(int argc, char *argv[])
{
        const int fd = open("/dev/char/4:1", O_RDWR);
        struct vt_sizes vt = { 0x4100, 2 };

        ioctl(fd, KDSETMODE, KD_GRAPHICS);
        ioctl(fd, VT_RESIZE, &vt);
        ioctl(fd, KDSETMODE, KD_TEXT);
        return 0;
}
----------

Allow framebuffer drivers to return -EINVAL, by moving
vc->vc_mode != KD_GRAPHICS check from resize_screen() to fbcon_resize().

[1] https://syzkaller.appspot.com/bug?extid=1f29e126cf461c4de3b3

Reported-by: syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>
---
 drivers/tty/vt/vt.c              | 2 +-
 drivers/video/fbdev/core/fbcon.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 01645e87b3d5..fa1548d4f94b 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1171,7 +1171,7 @@ static inline int resize_screen(struct vc_data *vc, int width, int height,
 	/* Resizes the resolution of the display adapater */
 	int err = 0;
 
-	if (vc->vc_mode != KD_GRAPHICS && vc->vc_sw->con_resize)
+	if (vc->vc_sw->con_resize)
 		err = vc->vc_sw->con_resize(vc, width, height, user);
 
 	return err;
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 3406067985b1..22bb3892f6bd 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2019,7 +2019,7 @@ static int fbcon_resize(struct vc_data *vc, unsigned int width,
 			return -EINVAL;
 
 		pr_debug("resize now %ix%i\n", var.xres, var.yres);
-		if (con_is_visible(vc)) {
+		if (con_is_visible(vc) && vc->vc_mode == KD_TEXT) {
 			var.activate = FB_ACTIVATE_NOW |
 				FB_ACTIVATE_FORCE;
 			fb_set_var(info, &var);
-- 
2.25.1


  reply	other threads:[~2021-05-15  7:44 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-19 17:33 BUG: unable to handle kernel paging request at ffffc90000669000, IP: [<ffffffff8139d84a>] bitfill_un Tommi Rantala
2019-12-10 16:38 ` BUG: unable to handle kernel paging request in sys_imageblit syzbot
2020-06-19  4:56   ` syzbot
2019-12-27  7:13 ` BUG: unable to handle kernel paging request in vga16fb_imageblit syzbot
2020-05-08  7:07 ` BUG: unable to handle kernel paging request in vga16fb_imageblit (2) syzbot
2021-05-01 20:31   ` [syzbot] " syzbot
2021-05-02  1:53   ` syzbot
2021-05-03 13:41     ` Tetsuo Handa
2021-05-07 11:09       ` Tetsuo Handa
2021-05-14 16:19         ` [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit() Tetsuo Handa
2021-05-14 17:29           ` Linus Torvalds
2021-05-14 17:37             ` Linus Torvalds
2021-05-14 18:23               ` Linus Torvalds
2021-05-14 20:25             ` Maciej W. Rozycki
2021-05-14 20:32               ` Linus Torvalds
2021-05-14 21:10                 ` Linus Torvalds
2021-05-15  7:43                   ` Tetsuo Handa [this message]
2021-05-15 16:21                     ` [PATCH v2] tty: vt: always invoke vc->vc_sw->con_resize callback Maciej W. Rozycki
2021-05-15 16:32                       ` Maciej W. Rozycki
2021-05-15 16:41                         ` Linus Torvalds
2021-05-17 13:13                           ` Daniel Vetter
2021-05-15 16:11                 ` [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit() Maciej W. Rozycki
2021-05-17 13:07                 ` Daniel Vetter
2021-05-17 13:10                   ` Daniel Vetter
2021-05-15  0:45               ` Tetsuo Handa
2020-05-12  6:55 ` BUG: unable to handle kernel paging request in bitfill_aligned syzbot
2020-10-06  8:18 ` BUG: unable to handle kernel paging request in cfb_imageblit syzbot
2020-12-18 15:26   ` syzbot
2020-12-18 15:27     ` Dmitry Vyukov

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