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, 148 insertions, 0 deletions

diff --git a/include/net/mrp.h b/include/net/mrp.h
new file mode 100644
index 000000000..b28915ffe
--- /dev/null
+++ b/include/net/mrp.h
@@ -0,0 +1,148 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_MRP_H
+#define _NET_MRP_H
+
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+
+#define MRP_END_MARK		0x0
+
+struct mrp_pdu_hdr {
+	u8	version;
+};
+
+struct mrp_msg_hdr {
+	u8	attrtype;
+	u8	attrlen;
+};
+
+struct mrp_vecattr_hdr {
+	__be16	lenflags;
+	unsigned char	firstattrvalue[];
+#define MRP_VECATTR_HDR_LEN_MASK cpu_to_be16(0x1FFF)
+#define MRP_VECATTR_HDR_FLAG_LA cpu_to_be16(0x2000)
+};
+
+enum mrp_vecattr_event {
+	MRP_VECATTR_EVENT_NEW,
+	MRP_VECATTR_EVENT_JOIN_IN,
+	MRP_VECATTR_EVENT_IN,
+	MRP_VECATTR_EVENT_JOIN_MT,
+	MRP_VECATTR_EVENT_MT,
+	MRP_VECATTR_EVENT_LV,
+	__MRP_VECATTR_EVENT_MAX
+};
+
+struct mrp_skb_cb {
+	struct mrp_msg_hdr	*mh;
+	struct mrp_vecattr_hdr	*vah;
+	unsigned char		attrvalue[];
+};
+
+static inline struct mrp_skb_cb *mrp_cb(struct sk_buff *skb)
+{
+	BUILD_BUG_ON(sizeof(struct mrp_skb_cb) >
+		     sizeof_field(struct sk_buff, cb));
+	return (struct mrp_skb_cb *)skb->cb;
+}
+
+enum mrp_applicant_state {
+	MRP_APPLICANT_INVALID,
+	MRP_APPLICANT_VO,
+	MRP_APPLICANT_VP,
+	MRP_APPLICANT_VN,
+	MRP_APPLICANT_AN,
+	MRP_APPLICANT_AA,
+	MRP_APPLICANT_QA,
+	MRP_APPLICANT_LA,
+	MRP_APPLICANT_AO,
+	MRP_APPLICANT_QO,
+	MRP_APPLICANT_AP,
+	MRP_APPLICANT_QP,
+	__MRP_APPLICANT_MAX
+};
+#define MRP_APPLICANT_MAX	(__MRP_APPLICANT_MAX - 1)
+
+enum mrp_event {
+	MRP_EVENT_NEW,
+	MRP_EVENT_JOIN,
+	MRP_EVENT_LV,
+	MRP_EVENT_TX,
+	MRP_EVENT_R_NEW,
+	MRP_EVENT_R_JOIN_IN,
+	MRP_EVENT_R_IN,
+	MRP_EVENT_R_JOIN_MT,
+	MRP_EVENT_R_MT,
+	MRP_EVENT_R_LV,
+	MRP_EVENT_R_LA,
+	MRP_EVENT_REDECLARE,
+	MRP_EVENT_PERIODIC,
+	__MRP_EVENT_MAX
+};
+#define MRP_EVENT_MAX		(__MRP_EVENT_MAX - 1)
+
+enum mrp_tx_action {
+	MRP_TX_ACTION_NONE,
+	MRP_TX_ACTION_S_NEW,
+	MRP_TX_ACTION_S_JOIN_IN,
+	MRP_TX_ACTION_S_JOIN_IN_OPTIONAL,
+	MRP_TX_ACTION_S_IN_OPTIONAL,
+	MRP_TX_ACTION_S_LV,
+};
+
+struct mrp_attr {
+	struct rb_node			node;
+	enum mrp_applicant_state	state;
+	u8				type;
+	u8				len;
+	unsigned char			value[];
+};
+
+enum mrp_applications {
+	MRP_APPLICATION_MVRP,
+	__MRP_APPLICATION_MAX
+};
+#define MRP_APPLICATION_MAX	(__MRP_APPLICATION_MAX - 1)
+
+struct mrp_application {
+	enum mrp_applications	type;
+	unsigned int		maxattr;
+	struct packet_type	pkttype;
+	unsigned char		group_address[ETH_ALEN];
+	u8			version;
+};
+
+struct mrp_applicant {
+	struct mrp_application	*app;
+	struct net_device	*dev;
+	struct timer_list	join_timer;
+	struct timer_list	periodic_timer;
+
+	spinlock_t		lock;
+	struct sk_buff_head	queue;
+	struct sk_buff		*pdu;
+	struct rb_root		mad;
+	struct rcu_head		rcu;
+	bool			active;
+};
+
+struct mrp_port {
+	struct mrp_applicant __rcu	*applicants[MRP_APPLICATION_MAX + 1];
+	struct rcu_head			rcu;
+};
+
+int mrp_register_application(struct mrp_application *app);
+void mrp_unregister_application(struct mrp_application *app);
+
+int mrp_init_applicant(struct net_device *dev, struct mrp_application *app);
+void mrp_uninit_applicant(struct net_device *dev, struct mrp_application *app);
+
+int mrp_request_join(const struct net_device *dev,
+		     const struct mrp_application *app,
+		     const void *value, u8 len, u8 type);
+void mrp_request_leave(const struct net_device *dev,
+		       const struct mrp_application *app,
+		       const void *value, u8 len, u8 type);
+
+#endif /* _NET_MRP_H */