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, 70 insertions, 0 deletions

diff --git a/net/ipv6/protocol.c b/net/ipv6/protocol.c
new file mode 100644
index 000000000..d4b1806ba
--- /dev/null
+++ b/net/ipv6/protocol.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * INET		An implementation of the TCP/IP protocol suite for the LINUX
+ *		operating system.  INET is implemented using the  BSD Socket
+ *		interface as the means of communication with the user level.
+ *
+ *		PF_INET6 protocol dispatch tables.
+ *
+ * Authors:	Pedro Roque	<roque@di.fc.ul.pt>
+ */
+
+/*
+ *      Changes:
+ *
+ *      Vince Laviano (vince@cs.stanford.edu)       16 May 2001
+ *      - Removed unused variable 'inet6_protocol_base'
+ *      - Modified inet6_del_protocol() to correctly maintain copy bit.
+ */
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/spinlock.h>
+#include <net/protocol.h>
+
+#if IS_ENABLED(CONFIG_IPV6)
+struct inet6_protocol __rcu *inet6_protos[MAX_INET_PROTOS] __read_mostly;
+EXPORT_SYMBOL(inet6_protos);
+
+int inet6_add_protocol(const struct inet6_protocol *prot, unsigned char protocol)
+{
+	return !cmpxchg((const struct inet6_protocol **)&inet6_protos[protocol],
+			NULL, prot) ? 0 : -1;
+}
+EXPORT_SYMBOL(inet6_add_protocol);
+
+int inet6_del_protocol(const struct inet6_protocol *prot, unsigned char protocol)
+{
+	int ret;
+
+	ret = (cmpxchg((const struct inet6_protocol **)&inet6_protos[protocol],
+		       prot, NULL) == prot) ? 0 : -1;
+
+	synchronize_net();
+
+	return ret;
+}
+EXPORT_SYMBOL(inet6_del_protocol);
+#endif
+
+const struct net_offload __rcu *inet6_offloads[MAX_INET_PROTOS] __read_mostly;
+EXPORT_SYMBOL(inet6_offloads);
+
+int inet6_add_offload(const struct net_offload *prot, unsigned char protocol)
+{
+	return !cmpxchg((const struct net_offload **)&inet6_offloads[protocol],
+			NULL, prot) ? 0 : -1;
+}
+EXPORT_SYMBOL(inet6_add_offload);
+
+int inet6_del_offload(const struct net_offload *prot, unsigned char protocol)
+{
+	int ret;
+
+	ret = (cmpxchg((const struct net_offload **)&inet6_offloads[protocol],
+		       prot, NULL) == prot) ? 0 : -1;
+
+	synchronize_net();
+
+	return ret;
+}
+EXPORT_SYMBOL(inet6_del_offload);