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, 26 insertions, 0 deletions

diff --git a/include/net/datalink.h b/include/net/datalink.h
new file mode 100644
index 000000000..6c529a40e
--- /dev/null
+++ b/include/net/datalink.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_INET_DATALINK_H_
+#define _NET_INET_DATALINK_H_
+
+#include <linux/list.h>
+
+struct llc_sap;
+struct net_device;
+struct packet_type;
+struct sk_buff;
+
+struct datalink_proto {
+        unsigned char   type[8];
+
+	struct llc_sap   *sap;
+
+        unsigned short  header_length;
+
+        int     (*rcvfunc)(struct sk_buff *, struct net_device *,
+                                struct packet_type *, struct net_device *);
+	int     (*request)(struct datalink_proto *, struct sk_buff *,
+			   const unsigned char *);
+	struct list_head node;
+};
+
+#endif