Messages in this thread | | | Date | Fri, 4 Jun 2021 15:19:43 +0200 | From | Greg KH <> | Subject | Re: [PATCH RFC] tty: Fix out-of-bound vmalloc access in imageblit |
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On Mon, May 31, 2021 at 09:47:13AM -0300, Igor Matheus Andrade Torrente wrote: > This issue happens when a userspace program does an ioctl > FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct > containing only the fields xres, yres, and bits_per_pixel > with values. > > If this struct is the same as the previous ioctl, the > vc_resize() detects it and doesn't call the resize_screen(), > leaving the fb_var_screeninfo incomplete. And this leads to > the updatescrollmode() calculates a wrong value to > fbcon_display->vrows, which makes the real_y() return a > wrong value of y, and that value, eventually, causes > the imageblit to access an out-of-bound address value. > > To solve this issue I brougth the resize_screen() the > beginning of vc_do_resize(), so it will "fix and fill" > the fb_var_screeninfo even if the screen does not need any > resizing. > > Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com > Signed-off-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com> > --- > drivers/tty/vt/vt.c | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c > index fa1548d4f94b..1b90758d8893 100644 > --- a/drivers/tty/vt/vt.c > +++ b/drivers/tty/vt/vt.c > @@ -1219,6 +1219,10 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc, > new_row_size = new_cols << 1; > new_screen_size = new_row_size * new_rows; > > + err = resize_screen(vc, new_cols, new_rows, user); > + if (err) > + return err; > + > if (new_cols == vc->vc_cols && new_rows == vc->vc_rows) > return 0; >
But now if any of the checks below this call fail, the screen will be resized and not "put back" to the original size, right? That could cause a mis-match of what is expected here.
thanks,
greg k-h
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