Re: [syzbot] BUG: unable to handle kernel paging request in vga16fb_imageblit (2)
From: Tetsuo Handa
Date: Fri May 07 2021 - 07:09:34 EST
On 2021/05/03 22:41, Tetsuo Handa wrote:
> Therefore, I guess that the problem is that fbcon_putcs() from do_update_region() from
> redraw_screen() from vt_kdsetmode(KD_TEXT) from ioctl(fd, KDSETMODE, KD_TEXT) tries to
> redraw 2 x 16640 despite memory amount allocated for actual screen is only 80 x 30.
>
> I don't know how to fix this problem...
>
Daniel Vetter suggested me that parameter validation is missing/wrong somewhere, for
resize requests that don't fit should be rejected. Thus, I'm thinking how to add
parameter validation.
Like a diff shown bottom, adding a hook for validating whether rows / columns are
small enough (VGA_FB_PHYS_LEN bytes starting from VGA_FB_PHYS ?) survives the
----------
#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;
}
----------
reproducer. But I don't know how to calculate upper boundary values for vga16fb_tty_resize(),
for I even don't know where these values are derived from...
Also, currently resize_screen() calls vc->vc_sw->con_resize() only if vc->vc_mode != KD_GRAPHICS.
But we need to unconditionally call vga16fb_tty_resize() in order to survive the reproducer; we
need to prevent vc->vc_{rows,cols} from exceeding the upper boundary values regardless of current
vc->vc_mode setting. The "vc->vc_mode != KD_GRAPHICS" check predates the git history, and I don't
know the side effect of removing this check...
----------
e400b6ec4ede4 drivers/char/vt.c (Antonino A. Daplas 2007-10-16 01:29:35 -0700 1168) static inline int resize_screen(struct vc_data *vc, int width, int height,
e400b6ec4ede4 drivers/char/vt.c (Antonino A. Daplas 2007-10-16 01:29:35 -0700 1169) int user)
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1170) {
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1171) /* Resizes the resolution of the display adapater */
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1172) int err = 0;
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1173)
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1174) if (vc->vc_mode != KD_GRAPHICS && vc->vc_sw->con_resize)
e400b6ec4ede4 drivers/char/vt.c (Antonino A. Daplas 2007-10-16 01:29:35 -0700 1175) err = vc->vc_sw->con_resize(vc, width, height, user);
e400b6ec4ede4 drivers/char/vt.c (Antonino A. Daplas 2007-10-16 01:29:35 -0700 1176)
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1177) return err;
^1da177e4c3f4 drivers/char/vt.c (Linus Torvalds 2005-04-16 15:20:36 -0700 1178) }
----------
I need more help from those who know this area.
drivers/tty/vt/vt.c | 2 +-
drivers/video/fbdev/core/fbcon.c | 7 +++++++
drivers/video/fbdev/vga16fb.c | 8 ++++++++
include/linux/fb.h | 3 +++
4 files changed, 19 insertions(+), 1 deletion(-)
----------
diff --git a/include/linux/fb.h b/include/linux/fb.h
index a8dccd23c249..870384afb5e9 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -289,14 +289,17 @@ struct fb_ops {
/* teardown any resources to do with this framebuffer */
void (*fb_destroy)(struct fb_info *info);
/* called at KDB enter and leave time to prepare the console */
int (*fb_debug_enter)(struct fb_info *info);
int (*fb_debug_leave)(struct fb_info *info);
+
+ /* Check if resizing TTY to these sizes is safe. */
+ int (*fb_tty_resize)(struct fb_info *info, unsigned int cols, unsigned int rows);
};
#ifdef CONFIG_FB_TILEBLITTING
#define FB_TILE_CURSOR_NONE 0
#define FB_TILE_CURSOR_UNDERLINE 1
#define FB_TILE_CURSOR_LOWER_THIRD 2
#define FB_TILE_CURSOR_LOWER_HALF 3
diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
index 1e8a38a7967d..54aa6a99b09c 100644
--- a/drivers/video/fbdev/vga16fb.c
+++ b/drivers/video/fbdev/vga16fb.c
@@ -1266,27 +1266,35 @@ static void vga16fb_destroy(struct fb_info *info)
{
iounmap(info->screen_base);
fb_dealloc_cmap(&info->cmap);
/* XXX unshare VGA regions */
framebuffer_release(info);
}
+static int vga16fb_tty_resize(struct fb_info *info, unsigned int cols, unsigned int rows)
+{
+ if (cols <= 80 && rows <= 30)
+ return 0;
+ return -EINVAL;
+}
+
static const struct fb_ops vga16fb_ops = {
.owner = THIS_MODULE,
.fb_open = vga16fb_open,
.fb_release = vga16fb_release,
.fb_destroy = vga16fb_destroy,
.fb_check_var = vga16fb_check_var,
.fb_set_par = vga16fb_set_par,
.fb_setcolreg = vga16fb_setcolreg,
.fb_pan_display = vga16fb_pan_display,
.fb_blank = vga16fb_blank,
.fb_fillrect = vga16fb_fillrect,
.fb_copyarea = vga16fb_copyarea,
.fb_imageblit = vga16fb_imageblit,
+ .fb_tty_resize = vga16fb_tty_resize,
};
#ifndef MODULE
static int __init vga16fb_setup(char *options)
{
char *this_opt;
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 3406067985b1..c0eac87a2a56 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1990,14 +1990,21 @@ static int fbcon_resize(struct vc_data *vc, unsigned int width,
if (pitch <= 0)
return -EINVAL;
size = CALC_FONTSZ(vc->vc_font.height, pitch, vc->vc_font.charcount);
if (size > FNTSIZE(vc->vc_font.data))
return -EINVAL;
}
+ if (info->fbops && info->fbops->fb_tty_resize) {
+ int err = info->fbops->fb_tty_resize(info, width, height);
+
+ if (err)
+ return err;
+ }
+
virt_w = FBCON_SWAP(ops->rotate, width, height);
virt_h = FBCON_SWAP(ops->rotate, height, width);
virt_fw = FBCON_SWAP(ops->rotate, vc->vc_font.width,
vc->vc_font.height);
virt_fh = FBCON_SWAP(ops->rotate, vc->vc_font.height,
vc->vc_font.width);
var.xres = virt_w * virt_fw;
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
@@ -1167,15 +1167,15 @@ int vc_allocate(unsigned int currcons) /* return 0 on success */
static inline int resize_screen(struct vc_data *vc, int width, int height,
int user)
{
/* 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;
}
/**
* vc_do_resize - resizing method for the tty
----------