| Message ID | 20220701202352.559808-3-deller@gmx.de (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | fbcon: Fixes for screen resolution changes - round 2 | expand |
Hi Helge, On Fri, Jul 1, 2022 at 10:23 PM Helge Deller <deller@gmx.de> wrote: > 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@gmx.de> > Cc: stable@vger.kernel.org # v5.4+ Thanks for your patch! > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -2736,6 +2736,34 @@ void fbcon_update_vcs(struct fb_info *info, bool all) > } > EXPORT_SYMBOL(fbcon_update_vcs); > > +/* 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; > + int i; unsigned int i > + > + WARN_CONSOLE_UNLOCKED(); > + > + if (!ops) > + return -EINVAL; This means the frame buffer device is not used as a text console (i.e. the text console is mapped to a different frame buffer device), hence it should return success. > + > + /* 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(fbcon_modechange_possible); EXPORT_SYMBOL_GPL()? No idea why most of fbcon uses the non-GPL variant. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index a33532564393..14b0ab51744f 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2736,6 +2736,34 @@ void fbcon_update_vcs(struct fb_info *info, bool all) } EXPORT_SYMBOL(fbcon_update_vcs); +/* 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; + int i; + + WARN_CONSOLE_UNLOCKED(); + + if (!ops) + return -EINVAL; + + /* 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(fbcon_modechange_possible); + 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 afa2863670f3..160389365a36 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1106,7 +1106,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, return -EFAULT; console_lock(); lock_fb_info(info); - ret = fb_set_var(info, &var); + ret = fbcon_modechange_possible(info, &var); + if (!ret) + ret = fb_set_var(info, &var); if (!ret) fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL); unlock_fb_info(info); diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h index ff5596dd30f8..2382dec6d6ab 100644 --- a/include/linux/fbcon.h +++ b/include/linux/fbcon.h @@ -15,6 +15,8 @@ void fbcon_new_modelist(struct fb_info *info); void fbcon_get_requirement(struct fb_info *info, struct fb_blit_caps *caps); void fbcon_fb_blanked(struct fb_info *info, int blank); +int fbcon_modechange_possible(struct fb_info *info, + struct fb_var_screeninfo *var); void fbcon_update_vcs(struct fb_info *info, bool all); void fbcon_remap_all(struct fb_info *info); int fbcon_set_con2fb_map_ioctl(void __user *argp); @@ -33,6 +35,8 @@ static inline void fbcon_new_modelist(struct fb_info *info) {} static inline void fbcon_get_requirement(struct fb_info *info, struct fb_blit_caps *caps) {} static inline void fbcon_fb_blanked(struct fb_info *info, int blank) {} +static inline int fbcon_modechange_possible(struct fb_info *info, + struct fb_var_screeninfo *var) { return 0; } static inline void fbcon_update_vcs(struct fb_info *info, bool all) {} static inline void fbcon_remap_all(struct fb_info *info) {} static inline int fbcon_set_con2fb_map_ioctl(void __user *argp) { return 0; }
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@gmx.de> Cc: stable@vger.kernel.org # v5.4+ --- drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++ drivers/video/fbdev/core/fbmem.c | 4 +++- include/linux/fbcon.h | 4 ++++ 3 files changed, 35 insertions(+), 1 deletion(-) -- 2.35.3