patch "vt: selection, handle pending signals in paste_selection" added to tty-linus

This is a note to let you know that I've just added the patch titled

vt: selection, handle pending signals in paste_selection

to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 687bff0cd08f790d540cfb7b2349f0d876cdddec Mon Sep 17 00:00:00 2001
From: Jiri Slaby <[email protected]>
Date: Mon, 10 Feb 2020 09:11:30 +0100
Subject: vt: selection, handle pending signals in paste_selection

When pasting a selection to a vt, the task is set as INTERRUPTIBLE while waiting for a tty to unthrottle. But signals are not handled at all. Normally, this is not a problem as tty_ldisc_receive_buf receives all the goods and a user has no reason to interrupt the task.

There are two scenarios where this matters:
1) when the tty is throttled and a signal is sent to the process, it spins on a CPU until the tty is unthrottled. schedule() does not really echedule, but returns immediately, of course.
2) when the sel_buffer becomes invalid, KASAN prevents any reads from it and the loop simply does not proceed and spins forever (causing the tty to throttle, but the code never sleeps, the same as above). This sometimes happens as there is a race in the sel_buffer handling code.

So add signal handling to this ioctl (TIOCL_PASTESEL) and return -EINTR in case a signal is pending.

---
 drivers/tty/vt/selection.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

index 78732feaf65b..44d974d4159f 100644
@@ -29,6 +29,8 @@
 #include <linux/console.h>
 #include <linux/tty_flip.h>
 
+#include <linux/sched/signal.h>
+
 /* Don't take this from <ctype.h>: 011-015 on the screen aren't spaces */
 #define isspace(c)	((c) == ' ')
 

@@ -350,6 +352,7 @@ int paste_selection(struct tty_struct *tty)
 	unsigned int count;
 	struct  tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
+	int ret = 0;
 
 	console_lock();
 	poke_blanked_console();

@@ -363,6 +366,10 @@ int paste_selection(struct tty_struct *tty)
 	add_wait_queue(&vc->paste_wait, &wait);
 	while (sel_buffer && sel_buffer_lth > pasted) {
 		set_current_state(TASK_INTERRUPTIBLE);
+		if (signal_pending(current)) {
+			ret = -EINTR;
+			break;
+		}
 		if (tty_throttled(tty)) {
 			schedule();
 			continue;

@@ -378,6 +385,6 @@ int paste_selection(struct tty_struct *tty)
 
 	tty_buffer_unlock_exclusive(&vc->port);
 	tty_ldisc_deref(ld);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(paste_selection);

2.25.0