openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 138 insertions, 0 deletions

diff --git a/drivers/md/dm-path-selector.c b/drivers/md/dm-path-selector.c
new file mode 100644
index 000000000..006a7991f
--- /dev/null
+++ b/drivers/md/dm-path-selector.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2003 Sistina Software.
+ * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
+ *
+ * Module Author: Heinz Mauelshagen
+ *
+ * This file is released under the GPL.
+ *
+ * Path selector registration.
+ */
+
+#include <linux/device-mapper.h>
+#include <linux/module.h>
+
+#include "dm-path-selector.h"
+
+#include <linux/slab.h>
+
+struct ps_internal {
+	struct path_selector_type pst;
+	struct list_head list;
+};
+
+#define pst_to_psi(__pst) container_of((__pst), struct ps_internal, pst)
+
+static LIST_HEAD(_path_selectors);
+static DECLARE_RWSEM(_ps_lock);
+
+static struct ps_internal *__find_path_selector_type(const char *name)
+{
+	struct ps_internal *psi;
+
+	list_for_each_entry(psi, &_path_selectors, list) {
+		if (!strcmp(name, psi->pst.name))
+			return psi;
+	}
+
+	return NULL;
+}
+
+static struct ps_internal *get_path_selector(const char *name)
+{
+	struct ps_internal *psi;
+
+	down_read(&_ps_lock);
+	psi = __find_path_selector_type(name);
+	if (psi && !try_module_get(psi->pst.module))
+		psi = NULL;
+	up_read(&_ps_lock);
+
+	return psi;
+}
+
+struct path_selector_type *dm_get_path_selector(const char *name)
+{
+	struct ps_internal *psi;
+
+	if (!name)
+		return NULL;
+
+	psi = get_path_selector(name);
+	if (!psi) {
+		request_module("dm-%s", name);
+		psi = get_path_selector(name);
+	}
+
+	return psi ? &psi->pst : NULL;
+}
+
+void dm_put_path_selector(struct path_selector_type *pst)
+{
+	struct ps_internal *psi;
+
+	if (!pst)
+		return;
+
+	down_read(&_ps_lock);
+	psi = __find_path_selector_type(pst->name);
+	if (!psi)
+		goto out;
+
+	module_put(psi->pst.module);
+out:
+	up_read(&_ps_lock);
+}
+
+static struct ps_internal *_alloc_path_selector(struct path_selector_type *pst)
+{
+	struct ps_internal *psi = kzalloc_obj(*psi);
+
+	if (psi)
+		psi->pst = *pst;
+
+	return psi;
+}
+
+int dm_register_path_selector(struct path_selector_type *pst)
+{
+	int r = 0;
+	struct ps_internal *psi = _alloc_path_selector(pst);
+
+	if (!psi)
+		return -ENOMEM;
+
+	down_write(&_ps_lock);
+
+	if (__find_path_selector_type(pst->name)) {
+		kfree(psi);
+		r = -EBUSY;
+	} else
+		list_add(&psi->list, &_path_selectors);
+
+	up_write(&_ps_lock);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_register_path_selector);
+
+void dm_unregister_path_selector(struct path_selector_type *pst)
+{
+	struct ps_internal *psi;
+
+	down_write(&_ps_lock);
+
+	psi = __find_path_selector_type(pst->name);
+	if (WARN_ON(!psi)) {
+		up_write(&_ps_lock);
+		return;
+	}
+
+	list_del(&psi->list);
+
+	up_write(&_ps_lock);
+
+	kfree(psi);
+}
+EXPORT_SYMBOL_GPL(dm_unregister_path_selector);