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, 72 insertions, 0 deletions

diff --git a/net/ipv4/fib_notifier.c b/net/ipv4/fib_notifier.c
new file mode 100644
index 000000000..b1551c265
--- /dev/null
+++ b/net/ipv4/fib_notifier.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/rtnetlink.h>
+#include <linux/notifier.h>
+#include <linux/socket.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <net/net_namespace.h>
+#include <net/fib_notifier.h>
+#include <net/ip_fib.h>
+
+int call_fib4_notifier(struct notifier_block *nb,
+		       enum fib_event_type event_type,
+		       struct fib_notifier_info *info)
+{
+	info->family = AF_INET;
+	return call_fib_notifier(nb, event_type, info);
+}
+
+int call_fib4_notifiers(struct net *net, enum fib_event_type event_type,
+			struct fib_notifier_info *info)
+{
+	ASSERT_RTNL();
+
+	info->family = AF_INET;
+	/* Paired with READ_ONCE() in fib4_seq_read() */
+	WRITE_ONCE(net->ipv4.fib_seq, net->ipv4.fib_seq + 1);
+	return call_fib_notifiers(net, event_type, info);
+}
+
+static unsigned int fib4_seq_read(const struct net *net)
+{
+	/* Paired with WRITE_ONCE() in call_fib4_notifiers() */
+	return READ_ONCE(net->ipv4.fib_seq) + fib4_rules_seq_read(net);
+}
+
+static int fib4_dump(struct net *net, struct notifier_block *nb,
+		     struct netlink_ext_ack *extack)
+{
+	int err;
+
+	err = fib4_rules_dump(net, nb, extack);
+	if (err)
+		return err;
+
+	return fib_notify(net, nb, extack);
+}
+
+static const struct fib_notifier_ops fib4_notifier_ops_template = {
+	.family		= AF_INET,
+	.fib_seq_read	= fib4_seq_read,
+	.fib_dump	= fib4_dump,
+	.owner		= THIS_MODULE,
+};
+
+int __net_init fib4_notifier_init(struct net *net)
+{
+	struct fib_notifier_ops *ops;
+
+	net->ipv4.fib_seq = 0;
+
+	ops = fib_notifier_ops_register(&fib4_notifier_ops_template, net);
+	if (IS_ERR(ops))
+		return PTR_ERR(ops);
+	net->ipv4.notifier_ops = ops;
+
+	return 0;
+}
+
+void __net_exit fib4_notifier_exit(struct net *net)
+{
+	fib_notifier_ops_unregister(net->ipv4.notifier_ops);
+}