[PATCH 6.6 104/213] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

6.6-stable review patch. If anyone has any objections, please let me know.

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From: Qianqiang Liu qianqiang.liu@163.com

[ Upstream commit 5b97eebcce1b4f3f07a71f635d6aa3af96c236e7 ]

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.

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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/video/fbdev/core/fbcon.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 24035b4f2cd70..405d587450ef8 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -847,6 +847,8 @@ static int set_con2fb_map(int unit, int newidx, int user) return err;

fbcon_add_cursor_work(info); + } else if (vc) { + set_blitting_type(vc, info); }

con2fb_map[unit] = newidx;