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, 56 insertions, 0 deletions

diff --git a/net/batman-adv/bitarray.h b/net/batman-adv/bitarray.h
new file mode 100644
index 000000000..2b9f5dbb3
--- /dev/null
+++ b/net/batman-adv/bitarray.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Simon Wunderlich, Marek Lindner
+ */
+
+#ifndef _NET_BATMAN_ADV_BITARRAY_H_
+#define _NET_BATMAN_ADV_BITARRAY_H_
+
+#include "main.h"
+
+#include <linux/bitops.h>
+#include <linux/compiler.h>
+#include <linux/stddef.h>
+#include <linux/types.h>
+
+/**
+ * batadv_test_bit() - check if bit is set in the current window
+ *
+ * @seq_bits: pointer to the sequence number bitmap of received packets
+ * @last_seqno: latest sequence number in seq_bits
+ * @curr_seqno: sequence number to test for
+ *
+ * Return: true if the corresponding bit in the given seq_bits indicates true
+ * and curr_seqno is within range of last_seqno. Otherwise returns false.
+ */
+static inline bool batadv_test_bit(const unsigned long *seq_bits,
+				   u32 last_seqno, u32 curr_seqno)
+{
+	s32 diff;
+
+	diff = last_seqno - curr_seqno;
+	if (diff < 0 || diff >= BATADV_TQ_LOCAL_WINDOW_SIZE)
+		return false;
+	return test_bit(diff, seq_bits) != 0;
+}
+
+/**
+ * batadv_set_bit() - Turn corresponding bit on, so we can remember that we got
+ *  the packet
+ * @seq_bits: bitmap of the packet receive window
+ * @n: relative sequence number of newly received packet
+ */
+static inline void batadv_set_bit(unsigned long *seq_bits, s32 n)
+{
+	/* if too old, just drop it */
+	if (n < 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE)
+		return;
+
+	set_bit(n, seq_bits); /* turn the position on */
+}
+
+bool batadv_bit_get_packet(void *priv, unsigned long *seq_bits,
+			   s32 seq_num_diff, int set_mark);
+
+#endif /* _NET_BATMAN_ADV_BITARRAY_H_ */