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, 36 insertions, 0 deletions

diff --git a/fs/adfs/file.c b/fs/adfs/file.c
new file mode 100644
index 000000000..d056d48c6
--- /dev/null
+++ b/fs/adfs/file.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/adfs/file.c
+ *
+ * Copyright (C) 1997-1999 Russell King
+ * from:
+ *
+ *  linux/fs/ext2/file.c
+ *
+ * Copyright (C) 1992, 1993, 1994, 1995
+ * Remy Card (card@masi.ibp.fr)
+ * Laboratoire MASI - Institut Blaise Pascal
+ * Universite Pierre et Marie Curie (Paris VI)
+ *
+ *  from
+ *
+ *  linux/fs/minix/file.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  adfs regular file handling primitives           
+ */
+#include "adfs.h"
+
+const struct file_operations adfs_file_operations = {
+	.llseek		= generic_file_llseek,
+	.read_iter	= generic_file_read_iter,
+	.mmap_prepare	= generic_file_mmap_prepare,
+	.fsync		= simple_fsync,
+	.write_iter	= generic_file_write_iter,
+	.splice_read	= filemap_splice_read,
+};
+
+const struct inode_operations adfs_file_inode_operations = {
+	.setattr	= adfs_setattr,
+};