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5b97eebcce
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, ¶m);
con2fb.console = 1;
con2fb.framebuffer = 0;
ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);
return 0;
}
After calling ioctl(fd1, TIOCLINUX, ¶m), 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.
Reported-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a
Tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com
Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.