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, 110 insertions, 0 deletions

diff --git a/fs/fuse/dev.h b/fs/fuse/dev.h
new file mode 100644
index 000000000..aed69fd14
--- /dev/null
+++ b/fs/fuse/dev.h
@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _FS_FUSE_DEV_H
+#define _FS_FUSE_DEV_H
+
+#include <linux/cleanup.h>
+
+/** Maximum number of outstanding background requests */
+#define FUSE_DEFAULT_MAX_BACKGROUND 12
+
+struct fuse_conn;
+struct fuse_chan;
+struct fuse_dev;
+struct fuse_args;
+struct fuse_copy_state;
+struct fuse_backing_map;
+struct file;
+struct folio;
+enum fuse_notify_code;
+
+struct fuse_chan_param {
+	unsigned int minor;
+	unsigned int max_write;
+	unsigned int max_pages;
+};
+
+struct fuse_chan *fuse_chan_new(void);
+struct fuse_chan *fuse_dev_chan_new(void);
+void fuse_chan_release(struct fuse_chan *fch);
+void fuse_chan_free(struct fuse_chan *fch);
+unsigned int fuse_chan_num_background(struct fuse_chan *fch);
+unsigned int fuse_chan_max_background(struct fuse_chan *fch);
+void fuse_chan_max_background_set(struct fuse_chan *fch, unsigned int val);
+unsigned int fuse_chan_num_waiting(struct fuse_chan *fch);
+void fuse_chan_set_fc(struct fuse_chan *fch, struct fuse_conn *fc);
+void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *param);
+void fuse_chan_io_uring_enable(struct fuse_chan *fch);
+ssize_t fuse_chan_send(struct fuse_chan *fch, struct fuse_args *args);
+int fuse_chan_send_bg(struct fuse_chan *fch, struct fuse_args *args, gfp_t gfp_flags);
+int fuse_chan_send_notify_reply(struct fuse_chan *fch, struct fuse_args *args, u64 unique);
+void fuse_chan_resend(struct fuse_chan *fch);
+
+struct fuse_forget_link *fuse_alloc_forget(void);
+void fuse_chan_queue_forget(struct fuse_chan *fch, struct fuse_forget_link *forget,
+			    u64 nodeid, u64 nlookup);
+
+DEFINE_FREE(fuse_chan_free, struct fuse_chan *, if (_T) fuse_chan_free(_T))
+
+/**
+ * Initialize the client device
+ */
+int fuse_dev_init(void);
+
+/**
+ * Cleanup the client device
+ */
+void fuse_dev_cleanup(void);
+
+void fuse_dev_install(struct fuse_dev *fud, struct fuse_chan *fch);
+bool fuse_dev_verify(struct fuse_dev *fud, struct fuse_chan *fch);
+void fuse_dev_put(struct fuse_dev *fud);
+bool fuse_dev_is_installed(struct fuse_dev *fud);
+bool fuse_dev_is_sync_init(struct fuse_dev *fud);
+struct fuse_dev *fuse_dev_grab(struct file *file);
+
+void fuse_init_server_timeout(struct fuse_chan *fch, unsigned int timeout);
+
+/* Abort all requests */
+void fuse_chan_abort(struct fuse_chan *fch, bool abort_with_err);
+void fuse_chan_wait_aborted(struct fuse_chan *fch);
+
+/**
+ * Acquire reference to fuse_conn
+ */
+struct fuse_conn *fuse_conn_get(struct fuse_conn *fc);
+
+/**
+ * Release reference to fuse_conn
+ */
+void fuse_conn_put(struct fuse_conn *fc);
+
+dev_t fuse_conn_get_id(struct fuse_conn *fc);
+
+void fuse_end_polls(struct fuse_conn *fc);
+int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
+		unsigned int size, struct fuse_copy_state *cs);
+
+int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map);
+int fuse_backing_close(struct fuse_conn *fc, int backing_id);
+
+int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size);
+int fuse_copy_folio(struct fuse_copy_state *cs, struct folio **foliop,
+		    unsigned offset, unsigned count, int zeroing);
+void fuse_copy_finish(struct fuse_copy_state *cs);
+
+#ifdef CONFIG_FUSE_IO_URING
+bool fuse_uring_enabled(void);
+void fuse_uring_destruct(struct fuse_chan *fch);
+#else /* CONFIG_FUSE_IO_URING */
+static inline bool fuse_uring_enabled(void)
+{
+	return false;
+}
+
+static inline void fuse_uring_destruct(struct fuse_chan *fch)
+{
+}
+#endif /* CONFIG_FUSE_IO_URING */
+
+#endif /* _FS_FUSE_DEV_H */