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, 52 insertions, 0 deletions

diff --git a/include/net/netns/generic.h b/include/net/netns/generic.h
new file mode 100644
index 000000000..00c399ede
--- /dev/null
+++ b/include/net/netns/generic.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * generic net pointers
+ */
+
+#ifndef __NET_GENERIC_H__
+#define __NET_GENERIC_H__
+
+#include <linux/bug.h>
+#include <linux/rcupdate.h>
+#include <net/net_namespace.h>
+
+/*
+ * Generic net pointers are to be used by modules to put some private
+ * stuff on the struct net without explicit struct net modification
+ *
+ * The rules are simple:
+ * 1. set pernet_operations->id.  After register_pernet_device you
+ *    will have the id of your private pointer.
+ * 2. set pernet_operations->size to have the code allocate and free
+ *    a private structure pointed to from struct net.
+ * 3. do not change this pointer while the net is alive;
+ * 4. do not try to have any private reference on the net_generic object.
+ *
+ * After accomplishing all of the above, the private pointer can be
+ * accessed with the net_generic() call.
+ */
+
+struct net_generic {
+	union {
+		struct {
+			unsigned int len;
+			struct rcu_head rcu;
+		} s;
+
+		DECLARE_FLEX_ARRAY(void *, ptr);
+	};
+};
+
+static inline void *net_generic(const struct net *net, unsigned int id)
+{
+	struct net_generic *ng;
+	void *ptr;
+
+	rcu_read_lock();
+	ng = rcu_dereference(net->gen);
+	ptr = ng->ptr[id];
+	rcu_read_unlock();
+
+	return ptr;
+}
+#endif