[PATCH] vt: keyboard: add NULL check for vc_cons[fg_console].d in kbd_keycode and kbd_rawcode

[Daniel Hodges <git@danielhodges.dev>]

kbd_keycode() and kbd_rawcode() dereference vc_cons[fg_console].d
without checking if it is NULL. The foreground console should normally
always be allocated, but there could be a time during console setup or
teardown where this pointer could be NULL, leading to a general
protection fault.

Syzkaller triggers this by injecting USB HID input events that reach
kbd_event() while the console state may not be fully consistent. The crash
manifests as a null-ptr-deref in __queue_work when put_queue() or
puts_queue() calls tty_flip_buffer_push() on the uninitialized vc port.

Add a NULL check for vc at the start of both kbd_rawcode() and
kbd_keycode() to bail out early if the foreground console is not allocated.

Reported-by: syzbot+c3693b491545af43db87@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c3693b491545af43db87
Reported-by: syzbot+03f79366754268a0f20c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=03f79366754268a0f20c
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Daniel Hodges <git@danielhodges.dev>
---
 drivers/tty/vt/keyboard.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index a2116e135a82..975830013d24 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1389,6 +1389,9 @@ static void kbd_rawcode(unsigned char data)
 {
 	struct vc_data *vc = vc_cons[fg_console].d;
 
+	if (!vc)
+		return;
+
 	kbd = &kbd_table[vc->vc_num];
 	if (kbd->kbdmode == VC_RAW)
 		put_queue(vc, data);
@@ -1405,6 +1408,9 @@ static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
 	struct keyboard_notifier_param param = { .vc = vc, .value = keycode, .down = down };
 	int rc;
 
+	if (!vc)
+		return;
+
 	tty = vc->port.tty;
 
 	if (tty && (!tty->driver_data)) {
-- 
2.52.0