Merge: CVE-2025-21746: Input: synaptics - fix crash when enabling pass-through port

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6451

JIRA: https://issues.redhat.com/browse/RHEL-81215
CVE: CVE-2025-21746

```
commit 08bd5b7
Author: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Date:   Fri Jan 17 09:23:40 2025 -0800

    Input: synaptics - fix crash when enabling pass-through port

    When enabling a pass-through port an interrupt might come before psmouse
    driver binds to the pass-through port. However synaptics sub-driver
    tries to access psmouse instance presumably associated with the
    pass-through port to figure out if only 1 byte of response or entire
    protocol packet needs to be forwarded to the pass-through port and may
    crash if psmouse instance has not been attached to the port yet.

    Fix the crash by introducing open() and close() methods for the port and
    check if the port is open before trying to access psmouse instance.
    Because psmouse calls serio_open() only after attaching psmouse instance
    to serio port instance this prevents the potential crash.

    Reported-by: Takashi Iwai <tiwai@suse.de>
    Fixes: 100e169 ("Input: libps2 - attach ps2dev instances as serio port's drvdata")
    Link: https://bugzilla.suse.com/show_bug.cgi?id=1219522
    Cc: stable@vger.kernel.org
    Reviewed-by: Takashi Iwai <tiwai@suse.de>
    Link: https://lore.kernel.org/r/Z4qSHORvPn7EU2j1@google.com
    Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>```

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

---

<small>Created 2025-02-27 14:14 UTC by backporter - [KWF FAQ](https://red.ht/kernel_workflow_doc) - [Slack #team-kernel-workflow](https://redhat-internal.slack.com/archives/C04LRUPMJQ5) - [Source](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/webhook/utils/backporter.py) - [Documentation](https://gitlab.com/cki-project/kernel-workflow/-/blob/main/docs/README.backporter.md) - [Report an issue](https://gitlab.com/cki-project/kernel-workflow/-/issues/new?issue%5Btitle%5D=backporter%20webhook%20issue)</small>

Approved-by: Jarod Wilson <jarod@redhat.com>
Approved-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Augusto Caringi <acaringi@redhat.com>

Author: caringi

drivers/input/mouse/synaptics.c

@@ -667,23 +667,50 @@ static void synaptics_pt_stop(struct serio *serio)
 	serio_continue_rx(parent->ps2dev.serio);
 }
 
+static int synaptics_pt_open(struct serio *serio)
+{
+	struct psmouse *parent = psmouse_from_serio(serio->parent);
+	struct synaptics_data *priv = parent->private;
+
+	guard(serio_pause_rx)(parent->ps2dev.serio);
+	priv->pt_port_open = true;
+
+	return 0;
+}
+
+static void synaptics_pt_close(struct serio *serio)
+{
+	struct psmouse *parent = psmouse_from_serio(serio->parent);
+	struct synaptics_data *priv = parent->private;
+
+	guard(serio_pause_rx)(parent->ps2dev.serio);
+	priv->pt_port_open = false;
+}
+
 static int synaptics_is_pt_packet(u8 *buf)
 {
 	return (buf[0] & 0xFC) == 0x84 && (buf[3] & 0xCC) == 0xC4;
 }
 
-static void synaptics_pass_pt_packet(struct serio *ptport, u8 *packet)
+static void synaptics_pass_pt_packet(struct synaptics_data *priv, u8 *packet)
 {
-	struct psmouse *child = psmouse_from_serio(ptport);
+	struct serio *ptport;
 
-	if (child && child->state == PSMOUSE_ACTIVATED) {
-		serio_interrupt(ptport, packet[1], 0);
-		serio_interrupt(ptport, packet[4], 0);
-		serio_interrupt(ptport, packet[5], 0);
-		if (child->pktsize == 4)
-			serio_interrupt(ptport, packet[2], 0);
-	} else {
-		serio_interrupt(ptport, packet[1], 0);
+	ptport = priv->pt_port;
+	if (!ptport)
+		return;
+
+	serio_interrupt(ptport, packet[1], 0);
+
+	if (priv->pt_port_open) {
+		struct psmouse *child = psmouse_from_serio(ptport);
+
+		if (child->state == PSMOUSE_ACTIVATED) {
+			serio_interrupt(ptport, packet[4], 0);
+			serio_interrupt(ptport, packet[5], 0);
+			if (child->pktsize == 4)
+				serio_interrupt(ptport, packet[2], 0);
+		}
 	}
 }
 
@@ -722,6 +749,8 @@ static void synaptics_pt_create(struct psmouse *psmouse)
 	serio->write = synaptics_pt_write;
 	serio->start = synaptics_pt_start;
 	serio->stop = synaptics_pt_stop;
+	serio->open = synaptics_pt_open;
+	serio->close = synaptics_pt_close;
 	serio->parent = psmouse->ps2dev.serio;
 
 	psmouse->pt_activate = synaptics_pt_activate;
@@ -1218,11 +1247,10 @@ static psmouse_ret_t synaptics_process_byte(struct psmouse *psmouse)
 
 		if (SYN_CAP_PASS_THROUGH(priv->info.capabilities) &&
 		    synaptics_is_pt_packet(psmouse->packet)) {
-			if (priv->pt_port)
-				synaptics_pass_pt_packet(priv->pt_port,
-							 psmouse->packet);
-		} else
+			synaptics_pass_pt_packet(priv, psmouse->packet);
+		} else {
 			synaptics_process_packet(psmouse);
+		}
 
 		return PSMOUSE_FULL_PACKET;
 	}

drivers/input/mouse/synaptics.h

@@ -188,6 +188,7 @@ struct synaptics_data {
 	bool disable_gesture;			/* disable gestures */
 
 	struct serio *pt_port;			/* Pass-through serio port */
+	bool pt_port_open;
 
 	/*
 	 * Last received Advanced Gesture Mode (AGM) packet. An AGM packet

include/linux/serio.h

@@ -6,6 +6,7 @@
 #define _SERIO_H
 
 
+#include <linux/cleanup.h>
 #include <linux/types.h>
 #include <linux/interrupt.h>
 #include <linux/list.h>
@@ -161,4 +162,6 @@ static inline void serio_continue_rx(struct serio *serio)
 	spin_unlock_irq(&serio->lock);
 }
 
+DEFINE_GUARD(serio_pause_rx, struct serio *, serio_pause_rx(_T), serio_continue_rx(_T))
+
 #endif