tty: vt: always invoke vc->vc_sw->con_resize callback

commit ffb324e6f874121f7dce5bdae5e05d02baae7269 upstream.

syzbot is reporting OOB write at vga16fb_imageblit() [1], for
resize_screen() from ioctl(VT_RESIZE) returns 0 without checking whether
requested rows/columns fit the amount of memory reserved for the graphical
screen if current mode is KD_GRAPHICS.

----------
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <sys/ioctl.h>
  #include <linux/kd.h>
  #include <linux/vt.h>

  int main(int argc, char *argv[])
  {
        const int fd = open("/dev/char/4:1", O_RDWR);
        struct vt_sizes vt = { 0x4100, 2 };

        ioctl(fd, KDSETMODE, KD_GRAPHICS);
        ioctl(fd, VT_RESIZE, &vt);
        ioctl(fd, KDSETMODE, KD_TEXT);
        return 0;
  }
----------

Allow framebuffer drivers to return -EINVAL, by moving vc->vc_mode !=
KD_GRAPHICS check from resize_screen() to fbcon_resize().

Link: https://syzkaller.appspot.com/bug?extid=1f29e126cf461c4de3b3
Reported-by: syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: syzbot <syzbot+1f29e126cf461c4de3b3@syzkaller.appspotmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 2fa7527b1230e8612dbd2f0934a22192b0566e89..8c74d9ebfc502147c0c2164c805d524a946cf49e 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -838,7 +838,7 @@ static inline int resize_screen(struct vc_data *vc, int width, int height,
        /* Resizes the resolution of the display adapater */
        int err = 0;
 
-       if (vc->vc_mode != KD_GRAPHICS && vc->vc_sw->con_resize)
+       if (vc->vc_sw->con_resize)
                err = vc->vc_sw->con_resize(vc, width, height, user);
 
        return err;

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 44df6f6fd063685d9647b6e64cd93cc423efcb60..510bc3f51dccfdf51a831a41837e7b6c22b4a059 100644 (file)
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -1986,7 +1986,7 @@ static int fbcon_resize(struct vc_data *vc, unsigned int width,
                        return -EINVAL;
 
                DPRINTK("resize now %ix%i\n", var.xres, var.yres);
-               if (con_is_visible(vc)) {
+               if (con_is_visible(vc) && vc->vc_mode == KD_TEXT) {
                        var.activate = FB_ACTIVATE_NOW |
                                FB_ACTIVATE_FORCE;
                        fb_set_var(info, &var);