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, 48 insertions, 0 deletions

diff --git a/include/net/dsa_stubs.h b/include/net/dsa_stubs.h
new file mode 100644
index 000000000..6f384897f
--- /dev/null
+++ b/include/net/dsa_stubs.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * include/net/dsa_stubs.h - Stubs for the Distributed Switch Architecture framework
+ */
+
+#include <linux/mutex.h>
+#include <linux/netdevice.h>
+#include <linux/net_tstamp.h>
+#include <net/dsa.h>
+
+#if IS_ENABLED(CONFIG_NET_DSA)
+
+extern const struct dsa_stubs *dsa_stubs;
+
+struct dsa_stubs {
+	int (*conduit_hwtstamp_validate)(struct net_device *dev,
+					 const struct kernel_hwtstamp_config *config,
+					 struct netlink_ext_ack *extack);
+};
+
+static inline int dsa_conduit_hwtstamp_validate(struct net_device *dev,
+						const struct kernel_hwtstamp_config *config,
+						struct netlink_ext_ack *extack)
+{
+	if (!netdev_uses_dsa(dev))
+		return 0;
+
+	/* rtnl_lock() is a sufficient guarantee, because as long as
+	 * netdev_uses_dsa() returns true, the dsa_core module is still
+	 * registered, and so, dsa_unregister_stubs() couldn't have run.
+	 * For netdev_uses_dsa() to start returning false, it would imply that
+	 * dsa_conduit_teardown() has executed, which requires rtnl_lock().
+	 */
+	ASSERT_RTNL();
+
+	return dsa_stubs->conduit_hwtstamp_validate(dev, config, extack);
+}
+
+#else
+
+static inline int dsa_conduit_hwtstamp_validate(struct net_device *dev,
+						const struct kernel_hwtstamp_config *config,
+						struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+#endif