CVE-2024-50048

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References