[PATCH stable 4.19 4.14 0/2] add fix patch for CVE-2021-3365

[PATCH stable 4.19 4.14 0/2] add fix patch for CVE-2021-3365

[Chen Jun]

refer to https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
3 patches are provided to fix CVE-2021-3365 (When sending malicous data
to kernel by ioctl cmd FBIOPUT_VSCREENINFO,kernel will write memory out
of bounds. https://nvd.nist.gov/vuln/detail/CVE-2021-33655) in mainline.

But only
commit 65a01e601dbb ("fbcon: Disallow setting font bigger than screen size")
was backported to stable (4.19,4.14).

without other two commit
commit e64242caef18 ("fbcon: Prevent that screen size is smaller than font size")
commit 6c11df58fd1a ("fbmem: Check virtual screen sizes in fb_set_var()")
The problem still exists.

static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
	fb_set_var(info, &var);
		fb_notifier_call_chain(evnt, &event); // evnt = FB_EVENT_MODE_CHANGE

static int fbcon_event_notify(struct notifier_block *self,
			      unsigned long action, void *data)
	fbcon_modechanged(info);
		updatescrollmode(p, info, vc);
			...
			p->vrows = vyres/fh;
			if (yres > (fh * (vc->vc_rows + 1)))
				p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
			if ((yres % fh) && (vyres % fh < yres % fh))
				p->vrows--;	[1]
[1]: p->vrows could be -1, like what CVE-2021-3365 described.

I think, the two commits should be backported to 4.19 and 4.14.

Helge Deller (2):
  fbcon: Prevent that screen size is smaller than font size
  fbmem: Check virtual screen sizes in fb_set_var()

 drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
 drivers/video/fbdev/core/fbmem.c | 20 +++++++++++++++++---
 include/linux/fbcon.h            |  4 ++++
 3 files changed, 49 insertions(+), 3 deletions(-)

-- 
2.17.1

[PATCH stable 4.19 4.14 1/2] fbcon: Prevent that screen size is smaller than font size

[Chen Jun]

From: Helge Deller <deller@gmx.de>

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@gmx.de>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
[sudip: adjust context]
Signed-off-by: Chen Jun <chenjun102@huawei.com>
---
 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 17ed20a73c2d..a55b3688b632 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2729,6 +2729,34 @@ 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 2297dfb494d6..b1733a2e0002 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1121,9 +1121,13 @@ 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);
 		console_unlock();
 		if (!ret && copy_to_user(argp, &var, sizeof(var)))
diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h
index f68a7db14165..39939d55c834 100644
--- a/include/linux/fbcon.h
+++ b/include/linux/fbcon.h
@@ -4,9 +4,13 @@
 #ifdef CONFIG_FRAMEBUFFER_CONSOLE
 void __init fb_console_init(void);
 void __exit fb_console_exit(void);
+int  fbcon_modechange_possible(struct fb_info *info,
+			       struct fb_var_screeninfo *var);
 #else
 static inline void fb_console_init(void) {}
 static inline void fb_console_exit(void) {}
+static inline int  fbcon_modechange_possible(struct fb_info *info,
+				struct fb_var_screeninfo *var) { return 0; }
 #endif
 
 #endif /* _LINUX_FBCON_H */
-- 
2.17.1

[PATCH stable 4.19 4.14 2/2] fbmem: Check virtual screen sizes in fb_set_var()

[Chen Jun]

From: Helge Deller <deller@gmx.de>

commit 6c11df58fd1ac0aefcb3b227f72769272b939e56 upstream

Verify that the fbdev or drm driver correctly adjusted the virtual
screen sizes. On failure report the failing driver and reject the screen
size change.

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
[sudip: adjust context]
Signed-off-by: Chen Jun <chenjun102@huawei.com>
---
 drivers/video/fbdev/core/fbmem.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index b1733a2e0002..a8574a2a466e 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1006,6 +1006,16 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 		if (ret)
 			goto done;
 
+		/* verify that virtual resolution >= physical resolution */
+		if (var->xres_virtual < var->xres ||
+		    var->yres_virtual < var->yres) {
+			pr_warn("WARNING: fbcon: Driver '%s' missed to adjust virtual screen size (%ux%u vs. %ux%u)\n",
+				info->fix.id,
+				var->xres_virtual, var->yres_virtual,
+				var->xres, var->yres);
+			return -EINVAL;
+		}
+
 		if ((var->activate & FB_ACTIVATE_MASK) == FB_ACTIVATE_NOW) {
 			struct fb_var_screeninfo old_var;
 			struct fb_videomode mode;
-- 
2.17.1

Re: [PATCH stable 4.19 4.14 0/2] add fix patch for CVE-2021-3365

[Greg KH]

On Fri, Jul 29, 2022 at 03:11:38AM +0000, Chen Jun wrote:
> refer to https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
> 3 patches are provided to fix CVE-2021-3365 (When sending malicous data
> to kernel by ioctl cmd FBIOPUT_VSCREENINFO,kernel will write memory out
> of bounds. https://nvd.nist.gov/vuln/detail/CVE-2021-33655) in mainline.
> 
> But only
> commit 65a01e601dbb ("fbcon: Disallow setting font bigger than screen size")
> was backported to stable (4.19,4.14).
> 
> without other two commit
> commit e64242caef18 ("fbcon: Prevent that screen size is smaller than font size")
> commit 6c11df58fd1a ("fbmem: Check virtual screen sizes in fb_set_var()")
> The problem still exists.
> 
> static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> 	fb_set_var(info, &var);
> 		fb_notifier_call_chain(evnt, &event); // evnt = FB_EVENT_MODE_CHANGE
> 
> static int fbcon_event_notify(struct notifier_block *self,
> 			      unsigned long action, void *data)
> 	fbcon_modechanged(info);
> 		updatescrollmode(p, info, vc);
> 			...
> 			p->vrows = vyres/fh;
> 			if (yres > (fh * (vc->vc_rows + 1)))
> 				p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
> 			if ((yres % fh) && (vyres % fh < yres % fh))
> 				p->vrows--;	[1]
> [1]: p->vrows could be -1, like what CVE-2021-3365 described.
> 
> I think, the two commits should be backported to 4.19 and 4.14.
> 
> Helge Deller (2):
>   fbcon: Prevent that screen size is smaller than font size
>   fbmem: Check virtual screen sizes in fb_set_var()
> 
>  drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
>  drivers/video/fbdev/core/fbmem.c | 20 +++++++++++++++++---
>  include/linux/fbcon.h            |  4 ++++
>  3 files changed, 49 insertions(+), 3 deletions(-)
> 
> -- 
> 2.17.1
> 

This breaks the build on 4.14.y, did you test it there?

The error is:
	ERROR: "is_console_locked" [drivers/video/fbdev/core/fb.ko] undefined!

Can you please fix this up and also do a 4.9.y version?

thanks,

greg k-h

Re: [PATCH stable 4.19 4.14 0/2] add fix patch for CVE-2021-3365

[chenjun (AM)]

在 2022/7/31 20:37, Greg KH 写道:
> On Fri, Jul 29, 2022 at 03:11:38AM +0000, Chen Jun wrote:
>> refer to https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
>> 3 patches are provided to fix CVE-2021-3365 (When sending malicous data
>> to kernel by ioctl cmd FBIOPUT_VSCREENINFO,kernel will write memory out
>> of bounds. https://nvd.nist.gov/vuln/detail/CVE-2021-33655) in mainline.
>>
>> But only
>> commit 65a01e601dbb ("fbcon: Disallow setting font bigger than screen size")
>> was backported to stable (4.19,4.14).
>>
>> without other two commit
>> commit e64242caef18 ("fbcon: Prevent that screen size is smaller than font size")
>> commit 6c11df58fd1a ("fbmem: Check virtual screen sizes in fb_set_var()")
>> The problem still exists.
>>
>> static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
>> 	fb_set_var(info, &var);
>> 		fb_notifier_call_chain(evnt, &event); // evnt = FB_EVENT_MODE_CHANGE
>>
>> static int fbcon_event_notify(struct notifier_block *self,
>> 			      unsigned long action, void *data)
>> 	fbcon_modechanged(info);
>> 		updatescrollmode(p, info, vc);
>> 			...
>> 			p->vrows = vyres/fh;
>> 			if (yres > (fh * (vc->vc_rows + 1)))
>> 				p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
>> 			if ((yres % fh) && (vyres % fh < yres % fh))
>> 				p->vrows--;	[1]
>> [1]: p->vrows could be -1, like what CVE-2021-3365 described.
>>
>> I think, the two commits should be backported to 4.19 and 4.14.
>>
>> Helge Deller (2):
>>    fbcon: Prevent that screen size is smaller than font size
>>    fbmem: Check virtual screen sizes in fb_set_var()
>>
>>   drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
>>   drivers/video/fbdev/core/fbmem.c | 20 +++++++++++++++++---
>>   include/linux/fbcon.h            |  4 ++++
>>   3 files changed, 49 insertions(+), 3 deletions(-)
>>
>> -- 
>> 2.17.1
>>
> 
> This breaks the build on 4.14.y, did you test it there?
> 
> The error is:
> 	ERROR: "is_console_locked" [drivers/video/fbdev/core/fb.ko] undefined!
> 

if CONFIG_FRAMEBUFFER_CONSOLE = M,
"d48de54a9dab printk: Export is_console_locked"  is needed, which merged 
in 4.19.

I will sent the patch.

> Can you please fix this up and also do a 4.9.y version?
> 

ok, I will do it.

> thanks,
> 
> greg k-h
> 


-- 
Regards
Chen Jun