On Fri, Aug 05, 2022 at 06:22:03AM +0000, chenjun (AM) wrote:
> 在 2022/8/5 14:09, Cengiz Can 写道:
> > On Thu, 2022-08-04 at 12:27 +0000, Chen Jun wrote:
> >> From: Helge Deller <deller@xxxxxx>
> >>
> >> commit e64242caef18b4a5840b0e7a9bff37abd4f4f933 upstream
> >>
> >> We need to prevent that users configure a screen size which is smaller than the
> >> currently selected font size. Otherwise rendering chars on the screen will
> >> access memory outside the graphics memory region.
> >>
> >> This patch adds a new function fbcon_modechange_possible() which
> >> implements this check and which later may be extended with other checks
> >> if necessary. The new function is called from the FBIOPUT_VSCREENINFO
> >> ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
> >> for a too small screen size.
> >>
> >> Signed-off-by: Helge Deller <deller@xxxxxx>
> >> Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> >> [Chen Jun: adjust context]
> >> Signed-off-by: Chen Jun <chenjun102@xxxxxxxxxx>
> >> ---
> >> drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
> >> drivers/video/fbdev/core/fbmem.c | 10 +++++++---
> >> include/linux/fbcon.h | 4 ++++
> >> 3 files changed, 39 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> >> index a97e94b1c84f..b84264e98929 100644
> >> --- a/drivers/video/fbdev/core/fbcon.c
> >> +++ b/drivers/video/fbdev/core/fbcon.c
> >> @@ -2706,6 +2706,34 @@ static void fbcon_set_all_vcs(struct fb_info *info)
> >> fbcon_modechanged(info);
> >> }
> >>
> >> +/* let fbcon check if it supports a new screen resolution */
> >> +int fbcon_modechange_possible(struct fb_info *info, struct fb_var_screeninfo *var)
> >> +{
> >> + struct fbcon_ops *ops = info->fbcon_par;
> >> + struct vc_data *vc;
> >> + unsigned int i;
> >> +
> >> + WARN_CONSOLE_UNLOCKED();
> >> +
> >> + if (!ops)
> >> + return 0;
> >> +
> >> + /* prevent setting a screen size which is smaller than font size */
> >> + for (i = first_fb_vc; i <= last_fb_vc; i++) {
> >> + vc = vc_cons[i].d;
> >> + if (!vc || vc->vc_mode != KD_TEXT ||
> >> + registered_fb[con2fb_map[i]] != info)
> >> + continue;
> >> +
> >> + if (vc->vc_font.width > FBCON_SWAP(var->rotate, var->xres, var->yres) ||
> >> + vc->vc_font.height > FBCON_SWAP(var->rotate, var->yres, var->xres))
> >> + return -EINVAL;
> >> + }
> >> +
> >> + return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(fbcon_modechange_possible);
> >> +
> >> static int fbcon_mode_deleted(struct fb_info *info,
> >> struct fb_videomode *mode)
> >> {
> >> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> >> index 9087d467cc46..264e8ca5efa7 100644
> >> --- a/drivers/video/fbdev/core/fbmem.c
> >> +++ b/drivers/video/fbdev/core/fbmem.c
> >> @@ -1134,9 +1134,13 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> >> console_unlock();
> >> return -ENODEV;
> >> }
> >> - info->flags |= FBINFO_MISC_USEREVENT;
> >> - ret = fb_set_var(info, &var);
> >> - info->flags &= ~FBINFO_MISC_USEREVENT;
> >> + ret = fbcon_modechange_possible(info, &var);
> >> + if (!ret) {
> >> + info->flags |= FBINFO_MISC_USEREVENT;
> >> + ret = fb_set_var(info, &var);
> >> + info->flags &= ~FBINFO_MISC_USEREVENT;
> >> + }
> >> + lock_fb_info(info);
> >> unlock_fb_info(info);
> >
> > Why do we lock and unlock here consecutively?
> >
> > Can it be a leftover?
> >
> > Because in upstream commit, lock encapsulates `fb_set_var`,
> > `fbcon_modechange_possible` and `fbcon_update_vcs` calls, which makes
> > sense.
> >
> > Here, it doesn't.
> >
>
> Thanks, lock_fb_info(info) is wrong here.
Ok, I'm totally confused now.
I'm dropping all of these series from my queue now. Please fix them up
and resend them for all pending stable trees (4.9.y, 4.14.y, and
4.19.y).
thanks,
greg k-h
