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, 42 insertions, 0 deletions

diff --git a/fs/autofs/init.c b/fs/autofs/init.c
new file mode 100644
index 000000000..1d644a35f
--- /dev/null
+++ b/fs/autofs/init.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include "autofs_i.h"
+
+struct file_system_type autofs_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "autofs",
+	.init_fs_context = autofs_init_fs_context,
+	.parameters	= autofs_param_specs,
+	.kill_sb	= autofs_kill_sb,
+};
+MODULE_ALIAS_FS("autofs");
+MODULE_ALIAS("autofs");
+
+static int __init init_autofs_fs(void)
+{
+	int err;
+
+	autofs_dev_ioctl_init();
+
+	err = register_filesystem(&autofs_fs_type);
+	if (err)
+		autofs_dev_ioctl_exit();
+
+	return err;
+}
+
+static void __exit exit_autofs_fs(void)
+{
+	autofs_dev_ioctl_exit();
+	unregister_filesystem(&autofs_fs_type);
+}
+
+module_init(init_autofs_fs)
+module_exit(exit_autofs_fs)
+MODULE_DESCRIPTION("Kernel automounter support");
+MODULE_LICENSE("GPL");