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, 207 insertions, 0 deletions

diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
new file mode 100644
index 000000000..6f88b507f
--- /dev/null
+++ b/security/keys/user_defined.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* user_defined.c: user defined key type
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+#include <linux/err.h>
+#include <keys/user-type.h>
+#include <linux/uaccess.h>
+#include "internal.h"
+
+static int logon_vet_description(const char *desc);
+
+/*
+ * user defined keys take an arbitrary string as the description and an
+ * arbitrary blob of data as the payload
+ */
+struct key_type key_type_user = {
+	.name			= "user",
+	.preparse		= user_preparse,
+	.free_preparse		= user_free_preparse,
+	.instantiate		= generic_key_instantiate,
+	.update			= user_update,
+	.revoke			= user_revoke,
+	.destroy		= user_destroy,
+	.describe		= user_describe,
+	.read			= user_read,
+};
+
+EXPORT_SYMBOL_GPL(key_type_user);
+
+/*
+ * This key type is essentially the same as key_type_user, but it does
+ * not define a .read op. This is suitable for storing username and
+ * password pairs in the keyring that you do not want to be readable
+ * from userspace.
+ */
+struct key_type key_type_logon = {
+	.name			= "logon",
+	.preparse		= user_preparse,
+	.free_preparse		= user_free_preparse,
+	.instantiate		= generic_key_instantiate,
+	.update			= user_update,
+	.revoke			= user_revoke,
+	.destroy		= user_destroy,
+	.describe		= user_describe,
+	.vet_description	= logon_vet_description,
+};
+EXPORT_SYMBOL_GPL(key_type_logon);
+
+/*
+ * Preparse a user defined key payload
+ */
+int user_preparse(struct key_preparsed_payload *prep)
+{
+	struct user_key_payload *upayload;
+	size_t datalen = prep->datalen;
+
+	if (datalen == 0 || datalen > 32767 || !prep->data)
+		return -EINVAL;
+
+	upayload = kmalloc_flex(*upayload, data, datalen);
+	if (!upayload)
+		return -ENOMEM;
+
+	/* attach the data */
+	prep->quotalen = datalen;
+	prep->payload.data[0] = upayload;
+	upayload->datalen = datalen;
+	memcpy(upayload->data, prep->data, datalen);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(user_preparse);
+
+/*
+ * Free a preparse of a user defined key payload
+ */
+void user_free_preparse(struct key_preparsed_payload *prep)
+{
+	kfree_sensitive(prep->payload.data[0]);
+}
+EXPORT_SYMBOL_GPL(user_free_preparse);
+
+static void user_free_payload_rcu(struct rcu_head *head)
+{
+	struct user_key_payload *payload;
+
+	payload = container_of(head, struct user_key_payload, rcu);
+	kfree_sensitive(payload);
+}
+
+/*
+ * update a user defined key
+ * - the key's semaphore is write-locked
+ */
+int user_update(struct key *key, struct key_preparsed_payload *prep)
+{
+	struct user_key_payload *zap = NULL;
+	int ret;
+
+	/* check the quota and attach the new data */
+	ret = key_payload_reserve(key, prep->datalen);
+	if (ret < 0)
+		return ret;
+
+	/* attach the new data, displacing the old */
+	key->expiry = prep->expiry;
+	if (key_is_positive(key))
+		zap = dereference_key_locked(key);
+	rcu_assign_keypointer(key, prep->payload.data[0]);
+	prep->payload.data[0] = NULL;
+
+	if (zap)
+		call_rcu(&zap->rcu, user_free_payload_rcu);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(user_update);
+
+/*
+ * dispose of the links from a revoked keyring
+ * - called with the key sem write-locked
+ */
+void user_revoke(struct key *key)
+{
+	struct user_key_payload *upayload = user_key_payload_locked(key);
+
+	/* clear the quota */
+	key_payload_reserve(key, 0);
+
+	if (upayload) {
+		rcu_assign_keypointer(key, NULL);
+		call_rcu(&upayload->rcu, user_free_payload_rcu);
+	}
+}
+
+EXPORT_SYMBOL(user_revoke);
+
+/*
+ * dispose of the data dangling from the corpse of a user key
+ */
+void user_destroy(struct key *key)
+{
+	struct user_key_payload *upayload = key->payload.data[0];
+
+	kfree_sensitive(upayload);
+}
+
+EXPORT_SYMBOL_GPL(user_destroy);
+
+/*
+ * describe the user key
+ */
+void user_describe(const struct key *key, struct seq_file *m)
+{
+	seq_puts(m, key->description);
+	if (key_is_positive(key))
+		seq_printf(m, ": %u", key->datalen);
+}
+
+EXPORT_SYMBOL_GPL(user_describe);
+
+/*
+ * read the key data
+ * - the key's semaphore is read-locked
+ */
+long user_read(const struct key *key, char *buffer, size_t buflen)
+{
+	const struct user_key_payload *upayload;
+	long ret;
+
+	upayload = user_key_payload_locked(key);
+	ret = upayload->datalen;
+
+	/* we can return the data as is */
+	if (buffer && buflen > 0) {
+		if (buflen > upayload->datalen)
+			buflen = upayload->datalen;
+
+		memcpy(buffer, upayload->data, buflen);
+	}
+
+	return ret;
+}
+
+EXPORT_SYMBOL_GPL(user_read);
+
+/* Vet the description for a "logon" key */
+static int logon_vet_description(const char *desc)
+{
+	char *p;
+
+	/* require a "qualified" description string */
+	p = strchr(desc, ':');
+	if (!p)
+		return -EINVAL;
+
+	/* also reject description with ':' as first char */
+	if (p == desc)
+		return -EINVAL;
+
+	return 0;
+}