linux-kernel - Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in fbcon

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Message-ID: <Zu2VCshU3Jx5X7oE@thinkpad.lan>
Date: Fri, 20 Sep 2024 23:30:18 +0800
From: Qianqiang Liu <qianqiang.liu@....com>
To: Helge Deller <deller@....de>
Cc: aniel@...ll.ch, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, stable@...r.kernel.org,
	syzbot+3d613ae53c031502687a@...kaller.appspotmail.com
Subject: Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in
 fbcon_putcs

Hi, 

I simplified the C reproducer as follows:

#include <stdint.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <linux/tiocl.h>
#include <sys/ioctl.h>

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

int main()
{
        write(1, "executing program\n", sizeof("executing program\n") - 1);

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

        struct fb_con2fbmap con2fb;
        con2fb.console = 0x19;
        con2fb.framebuffer = 0;
        ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);

        int fd1 = open("/dev/tty1", O_RDWR, 0);

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

        ioctl(fd1, TIOCLINUX, &param);

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

        return 0;
}

But I still need time to debug the kernel code..

-- 
Best,
Qianqiang Liu