Subject: CVE-2024-50048: fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

syzbot has found a NULL pointer dereference bug in fbcon.
Here is the simplified C reproducer:

struct param {
	uint8_t type;
	struct tiocl_selection ts;
};

int main()
{
	struct fb_con2fbmap con2fb;
	struct param param;

	int fd = open("/dev/fb1", 0, 0);

	con2fb.console = 0x19;
	con2fb.framebuffer = 0;
	ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);

	param.type = 2;
	param.ts.xs = 0; param.ts.ys = 0;
	param.ts.xe = 0; param.ts.ye = 0;
	param.ts.sel_mode = 0;

	int fd1 = open("/dev/tty1", O_RDWR, 0);
	ioctl(fd1, TIOCLINUX, &param);

	con2fb.console = 1;
	con2fb.framebuffer = 0;
	ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);

	return 0;
}

After calling ioctl(fd1, TIOCLINUX, &param), the subsequent ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb)
causes the kernel to follow a different execution path:

 set_con2fb_map
  -> con2fb_init_display
   -> fbcon_set_disp
    -> redraw_screen
     -> hide_cursor
      -> clear_selection
       -> highlight
        -> invert_screen
         -> do_update_region
          -> fbcon_putcs
           -> ops->putcs

Since ops->putcs is a NULL pointer, this leads to a kernel panic.
To prevent this, we need to call set_blitting_type() within set_con2fb_map()
to properly initialize ops->putcs.

The Linux kernel CVE team has assigned CVE-2024-50048 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.1.113 with commit 8266ae6eafdc
	Fixed in 6.6.57 with commit f7fb5dda5553
	Fixed in 6.11.4 with commit e5c2dba62996
	Fixed in 6.12-rc1 with commit 5b97eebcce1b

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-50048
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/video/fbdev/core/fbcon.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/8266ae6eafdcd5a3136592445ff4038bbc7ee80e
	https://git.kernel.org/stable/c/f7fb5dda555344529ce584ff7a28b109528d2f1b
	https://git.kernel.org/stable/c/e5c2dba62996a3a6eeb34bd248b90fc69c5a6a1b
	https://git.kernel.org/stable/c/5b97eebcce1b4f3f07a71f635d6aa3af96c236e7