1 files changed, 38 insertions, 10 deletions

diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c
index 2384ea85ffaf..160f46115aaa 100644
--- a/drivers/tty/vt/vc_screen.c
+++ b/drivers/tty/vt/vc_screen.c
@@ -80,7 +80,7 @@
 struct vcs_poll_data {
 	struct notifier_block notifier;
 	unsigned int cons_num;
-	bool seen_last_update;
+	int event;
 	wait_queue_head_t waitq;
 	struct fasync_struct *fasync;
 };
@@ -93,9 +93,18 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
 	struct vcs_poll_data *poll =
 		container_of(nb, struct vcs_poll_data, notifier);
 	int currcons = poll->cons_num;
-
-	if (code != VT_UPDATE)
+	int fa_band;
+
+	switch (code) {
+	case VT_UPDATE:
+		fa_band = POLL_PRI;
+		break;
+	case VT_DEALLOCATE:
+		fa_band = POLL_HUP;
+		break;
+	default:
 		return NOTIFY_DONE;
+	}
 
 	if (currcons == 0)
 		currcons = fg_console;
@@ -104,9 +113,9 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
 	if (currcons != vc->vc_num)
 		return NOTIFY_DONE;
 
-	poll->seen_last_update = false;
+	poll->event = code;
 	wake_up_interruptible(&poll->waitq);
-	kill_fasync(&poll->fasync, SIGIO, POLL_IN);
+	kill_fasync(&poll->fasync, SIGIO, fa_band);
 	return NOTIFY_OK;
 }
 
@@ -131,6 +140,15 @@ vcs_poll_data_get(struct file *file)
 	poll->cons_num = console(file_inode(file));
 	init_waitqueue_head(&poll->waitq);
 	poll->notifier.notifier_call = vcs_notifier;
+	/*
+	 * In order not to lose any update event, we must pretend one might
+	 * have occurred before we have a chance to register our notifier.
+	 * This is also how user space has come to detect which kernels
+	 * support POLLPRI on /dev/vcs* devices i.e. using poll() with
+	 * POLLPRI and a zero timeout.
+	 */
+	poll->event = VT_UPDATE;
+
 	if (register_vt_notifier(&poll->notifier) != 0) {
 		kfree(poll);
 		return NULL;
@@ -261,7 +279,7 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 
 	poll = file->private_data;
 	if (count && poll)
-		poll->seen_last_update = true;
+		poll->event = 0;
 	read = 0;
 	ret = 0;
 	while (count) {
@@ -335,8 +353,9 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 			if (p < HEADER_SIZE) {
 				size_t tmp_count;
 
-				con_buf0[0] = (char)vc->vc_rows;
-				con_buf0[1] = (char)vc->vc_cols;
+				/* clamp header values if they don't fit */
+				con_buf0[0] = min(vc->vc_rows, 0xFFu);
+				con_buf0[1] = min(vc->vc_cols, 0xFFu);
 				getconsxy(vc, con_buf0 + 2);
 
 				con_buf_start += p;
@@ -615,12 +634,21 @@ static __poll_t
 vcs_poll(struct file *file, poll_table *wait)
 {
 	struct vcs_poll_data *poll = vcs_poll_data_get(file);
-	__poll_t ret = DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
+	__poll_t ret = DEFAULT_POLLMASK|EPOLLERR;
 
 	if (poll) {
 		poll_wait(file, &poll->waitq, wait);
-		if (poll->seen_last_update)
+		switch (poll->event) {
+		case VT_UPDATE:
+			ret = DEFAULT_POLLMASK|EPOLLPRI;
+			break;
+		case VT_DEALLOCATE:
+			ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;
+			break;
+		case 0:
 			ret = DEFAULT_POLLMASK;
+			break;
+		}
 	}
 	return ret;
 }