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, 61 insertions, 0 deletions

diff --git a/include/net/wext.h b/include/net/wext.h
new file mode 100644
index 000000000..aa192a670
--- /dev/null
+++ b/include/net/wext.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_WEXT_H
+#define __NET_WEXT_H
+
+#include <net/iw_handler.h>
+
+struct net;
+
+#ifdef CONFIG_WEXT_CORE
+int wext_handle_ioctl(struct net *net, unsigned int cmd,
+		      void __user *arg);
+int compat_wext_handle_ioctl(struct net *net, unsigned int cmd,
+			     unsigned long arg);
+
+struct iw_statistics *get_wireless_stats(struct net_device *dev);
+int call_commit_handler(struct net_device *dev);
+#else
+static inline int wext_handle_ioctl(struct net *net, unsigned int cmd,
+				    void __user *arg)
+{
+	return -EINVAL;
+}
+static inline int compat_wext_handle_ioctl(struct net *net, unsigned int cmd,
+					   unsigned long arg)
+{
+	return -EINVAL;
+}
+#endif
+
+#ifdef CONFIG_WEXT_PROC
+int wext_proc_init(struct net *net);
+void wext_proc_exit(struct net *net);
+#else
+static inline int wext_proc_init(struct net *net)
+{
+	return 0;
+}
+static inline void wext_proc_exit(struct net *net)
+{
+	return;
+}
+#endif
+
+#ifdef CONFIG_WEXT_PRIV
+int ioctl_private_call(struct net_device *dev, struct iwreq *iwr,
+		       unsigned int cmd, struct iw_request_info *info,
+		       iw_handler handler);
+int compat_private_call(struct net_device *dev, struct iwreq *iwr,
+			unsigned int cmd, struct iw_request_info *info,
+			iw_handler handler);
+int iw_handler_get_private(struct net_device *		dev,
+			   struct iw_request_info *	info,
+			   union iwreq_data *		wrqu,
+			   char *			extra);
+#else
+#define ioctl_private_call NULL
+#define compat_private_call NULL
+#endif
+
+
+#endif /* __NET_WEXT_H */