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, 117 insertions, 0 deletions

diff --git a/fs/ceph/cache.h b/fs/ceph/cache.h
new file mode 100644
index 000000000..20efac020
--- /dev/null
+++ b/fs/ceph/cache.h
@@ -0,0 +1,117 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Ceph cache definitions.
+ *
+ *  Copyright (C) 2013 by Adfin Solutions, Inc. All Rights Reserved.
+ *  Written by Milosz Tanski (milosz@adfin.com)
+ */
+
+#ifndef _CEPH_CACHE_H
+#define _CEPH_CACHE_H
+
+#include <linux/netfs.h>
+
+#ifdef CONFIG_CEPH_FSCACHE
+#include <linux/fscache.h>
+
+int ceph_fscache_register_fs(struct ceph_fs_client* fsc, struct fs_context *fc);
+void ceph_fscache_unregister_fs(struct ceph_fs_client* fsc);
+
+void ceph_fscache_register_inode_cookie(struct inode *inode);
+void ceph_fscache_unregister_inode_cookie(struct ceph_inode_info* ci);
+
+void ceph_fscache_use_cookie(struct inode *inode, bool will_modify);
+void ceph_fscache_unuse_cookie(struct inode *inode, bool update);
+
+void ceph_fscache_update(struct inode *inode);
+void ceph_fscache_invalidate(struct inode *inode, bool dio_write);
+
+static inline struct fscache_cookie *ceph_fscache_cookie(struct ceph_inode_info *ci)
+{
+	return netfs_i_cookie(&ci->netfs);
+}
+
+static inline void ceph_fscache_resize(struct inode *inode, loff_t to)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct fscache_cookie *cookie = ceph_fscache_cookie(ci);
+
+	if (cookie) {
+		ceph_fscache_use_cookie(inode, true);
+		fscache_resize_cookie(cookie, to);
+		ceph_fscache_unuse_cookie(inode, true);
+	}
+}
+
+static inline int ceph_fscache_unpin_writeback(struct inode *inode,
+						struct writeback_control *wbc)
+{
+	return netfs_unpin_writeback(inode, wbc);
+}
+
+#define ceph_fscache_dirty_folio netfs_dirty_folio
+
+static inline bool ceph_is_cache_enabled(struct inode *inode)
+{
+	return fscache_cookie_enabled(ceph_fscache_cookie(ceph_inode(inode)));
+}
+
+#else /* CONFIG_CEPH_FSCACHE */
+static inline int ceph_fscache_register_fs(struct ceph_fs_client* fsc,
+					   struct fs_context *fc)
+{
+	return 0;
+}
+
+static inline void ceph_fscache_unregister_fs(struct ceph_fs_client* fsc)
+{
+}
+
+static inline void ceph_fscache_register_inode_cookie(struct inode *inode)
+{
+}
+
+static inline void ceph_fscache_unregister_inode_cookie(struct ceph_inode_info* ci)
+{
+}
+
+static inline void ceph_fscache_use_cookie(struct inode *inode, bool will_modify)
+{
+}
+
+static inline void ceph_fscache_unuse_cookie(struct inode *inode, bool update)
+{
+}
+
+static inline void ceph_fscache_update(struct inode *inode)
+{
+}
+
+static inline void ceph_fscache_invalidate(struct inode *inode, bool dio_write)
+{
+}
+
+static inline struct fscache_cookie *ceph_fscache_cookie(struct ceph_inode_info *ci)
+{
+	return NULL;
+}
+
+static inline void ceph_fscache_resize(struct inode *inode, loff_t to)
+{
+}
+
+static inline int ceph_fscache_unpin_writeback(struct inode *inode,
+					       struct writeback_control *wbc)
+{
+	return 0;
+}
+
+#define ceph_fscache_dirty_folio filemap_dirty_folio
+
+static inline bool ceph_is_cache_enabled(struct inode *inode)
+{
+	return false;
+}
+#endif /* CONFIG_CEPH_FSCACHE */
+
+#endif