ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 206 insertions, 0 deletions

diff --git a/net/lapb/lapb_timer.c b/net/lapb/lapb_timer.c
new file mode 100644
index 000000000..9fde6cf20
--- /dev/null
+++ b/net/lapb/lapb_timer.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	LAPB release 002
+ *
+ *	This code REQUIRES 2.1.15 or higher/ NET3.038
+ *
+ *	History
+ *	LAPB 001	Jonathan Naylor	Started Coding
+ *	LAPB 002	Jonathan Naylor	New timer architecture.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/in.h>
+#include <linux/kernel.h>
+#include <linux/jiffies.h>
+#include <linux/timer.h>
+#include <linux/string.h>
+#include <linux/sockios.h>
+#include <linux/net.h>
+#include <linux/inet.h>
+#include <linux/skbuff.h>
+#include <net/sock.h>
+#include <linux/uaccess.h>
+#include <linux/fcntl.h>
+#include <linux/mm.h>
+#include <linux/interrupt.h>
+#include <net/lapb.h>
+
+static void lapb_t1timer_expiry(struct timer_list *);
+static void lapb_t2timer_expiry(struct timer_list *);
+
+void lapb_start_t1timer(struct lapb_cb *lapb)
+{
+	timer_delete(&lapb->t1timer);
+
+	lapb->t1timer.function = lapb_t1timer_expiry;
+	lapb->t1timer.expires  = jiffies + lapb->t1;
+
+	lapb->t1timer_running = true;
+	add_timer(&lapb->t1timer);
+}
+
+void lapb_start_t2timer(struct lapb_cb *lapb)
+{
+	timer_delete(&lapb->t2timer);
+
+	lapb->t2timer.function = lapb_t2timer_expiry;
+	lapb->t2timer.expires  = jiffies + lapb->t2;
+
+	lapb->t2timer_running = true;
+	add_timer(&lapb->t2timer);
+}
+
+void lapb_stop_t1timer(struct lapb_cb *lapb)
+{
+	lapb->t1timer_running = false;
+	timer_delete(&lapb->t1timer);
+}
+
+void lapb_stop_t2timer(struct lapb_cb *lapb)
+{
+	lapb->t2timer_running = false;
+	timer_delete(&lapb->t2timer);
+}
+
+int lapb_t1timer_running(struct lapb_cb *lapb)
+{
+	return lapb->t1timer_running;
+}
+
+static void lapb_t2timer_expiry(struct timer_list *t)
+{
+	struct lapb_cb *lapb = timer_container_of(lapb, t, t2timer);
+
+	spin_lock_bh(&lapb->lock);
+	if (timer_pending(&lapb->t2timer)) /* A new timer has been set up */
+		goto out;
+	if (!lapb->t2timer_running) /* The timer has been stopped */
+		goto out;
+
+	if (lapb->condition & LAPB_ACK_PENDING_CONDITION) {
+		lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
+		lapb_timeout_response(lapb);
+	}
+	lapb->t2timer_running = false;
+
+out:
+	spin_unlock_bh(&lapb->lock);
+}
+
+static void lapb_t1timer_expiry(struct timer_list *t)
+{
+	struct lapb_cb *lapb = timer_container_of(lapb, t, t1timer);
+
+	spin_lock_bh(&lapb->lock);
+	if (timer_pending(&lapb->t1timer)) /* A new timer has been set up */
+		goto out;
+	if (!lapb->t1timer_running) /* The timer has been stopped */
+		goto out;
+
+	switch (lapb->state) {
+
+		/*
+		 *	If we are a DCE, send DM up to N2 times, then switch to
+		 *	STATE_1 and send SABM(E).
+		 */
+		case LAPB_STATE_0:
+			if (lapb->mode & LAPB_DCE &&
+			    lapb->n2count != lapb->n2) {
+				lapb->n2count++;
+				lapb_send_control(lapb, LAPB_DM, LAPB_POLLOFF, LAPB_RESPONSE);
+			} else {
+				lapb->state = LAPB_STATE_1;
+				lapb_establish_data_link(lapb);
+			}
+			break;
+
+		/*
+		 *	Awaiting connection state, send SABM(E), up to N2 times.
+		 */
+		case LAPB_STATE_1:
+			if (lapb->n2count == lapb->n2) {
+				lapb_clear_queues(lapb);
+				lapb->state = LAPB_STATE_0;
+				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
+				lapb_dbg(0, "(%p) S1 -> S0\n", lapb->dev);
+				lapb->t1timer_running = false;
+				goto out;
+			} else {
+				lapb->n2count++;
+				if (lapb->mode & LAPB_EXTENDED) {
+					lapb_dbg(1, "(%p) S1 TX SABME(1)\n",
+						 lapb->dev);
+					lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND);
+				} else {
+					lapb_dbg(1, "(%p) S1 TX SABM(1)\n",
+						 lapb->dev);
+					lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND);
+				}
+			}
+			break;
+
+		/*
+		 *	Awaiting disconnection state, send DISC, up to N2 times.
+		 */
+		case LAPB_STATE_2:
+			if (lapb->n2count == lapb->n2) {
+				lapb_clear_queues(lapb);
+				lapb->state = LAPB_STATE_0;
+				lapb_disconnect_confirmation(lapb, LAPB_TIMEDOUT);
+				lapb_dbg(0, "(%p) S2 -> S0\n", lapb->dev);
+				lapb->t1timer_running = false;
+				goto out;
+			} else {
+				lapb->n2count++;
+				lapb_dbg(1, "(%p) S2 TX DISC(1)\n", lapb->dev);
+				lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND);
+			}
+			break;
+
+		/*
+		 *	Data transfer state, restransmit I frames, up to N2 times.
+		 */
+		case LAPB_STATE_3:
+			if (lapb->n2count == lapb->n2) {
+				lapb_clear_queues(lapb);
+				lapb->state = LAPB_STATE_0;
+				lapb_stop_t2timer(lapb);
+				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
+				lapb_dbg(0, "(%p) S3 -> S0\n", lapb->dev);
+				lapb->t1timer_running = false;
+				goto out;
+			} else {
+				lapb->n2count++;
+				lapb_requeue_frames(lapb);
+				lapb_kick(lapb);
+			}
+			break;
+
+		/*
+		 *	Frame reject state, restransmit FRMR frames, up to N2 times.
+		 */
+		case LAPB_STATE_4:
+			if (lapb->n2count == lapb->n2) {
+				lapb_clear_queues(lapb);
+				lapb->state = LAPB_STATE_0;
+				lapb_disconnect_indication(lapb, LAPB_TIMEDOUT);
+				lapb_dbg(0, "(%p) S4 -> S0\n", lapb->dev);
+				lapb->t1timer_running = false;
+				goto out;
+			} else {
+				lapb->n2count++;
+				lapb_transmit_frmr(lapb);
+			}
+			break;
+	}
+
+	lapb_start_t1timer(lapb);
+
+out:
+	spin_unlock_bh(&lapb->lock);
+}