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

[Chen Jun <chenjun102@huawei.com>]

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(-)

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2.17.1