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, 123 insertions, 0 deletions

diff --git a/security/keys/permission.c b/security/keys/permission.c
new file mode 100644
index 000000000..4a61f804e
--- /dev/null
+++ b/security/keys/permission.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Key permission checking
+ *
+ * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/security.h>
+#include "internal.h"
+
+/**
+ * key_task_permission - Check a key can be used
+ * @key_ref: The key to check.
+ * @cred: The credentials to use.
+ * @need_perm: The permission required.
+ *
+ * Check to see whether permission is granted to use a key in the desired way,
+ * but permit the security modules to override.
+ *
+ * The caller must hold either a ref on cred or must hold the RCU readlock.
+ *
+ * Returns 0 if successful, -EACCES if access is denied based on the
+ * permissions bits or the LSM check.
+ */
+int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
+			enum key_need_perm need_perm)
+{
+	struct key *key;
+	key_perm_t kperm, mask;
+	int ret;
+
+	switch (need_perm) {
+	default:
+		WARN_ON(1);
+		return -EACCES;
+	case KEY_NEED_UNLINK:
+	case KEY_SYSADMIN_OVERRIDE:
+	case KEY_AUTHTOKEN_OVERRIDE:
+	case KEY_DEFER_PERM_CHECK:
+		goto lsm;
+
+	case KEY_NEED_VIEW:	mask = KEY_OTH_VIEW;	break;
+	case KEY_NEED_READ:	mask = KEY_OTH_READ;	break;
+	case KEY_NEED_WRITE:	mask = KEY_OTH_WRITE;	break;
+	case KEY_NEED_SEARCH:	mask = KEY_OTH_SEARCH;	break;
+	case KEY_NEED_LINK:	mask = KEY_OTH_LINK;	break;
+	case KEY_NEED_SETATTR:	mask = KEY_OTH_SETATTR;	break;
+	}
+
+	key = key_ref_to_ptr(key_ref);
+
+	/* use the second 8-bits of permissions for keys the caller owns */
+	if (uid_eq(key->uid, cred->fsuid)) {
+		kperm = key->perm >> 16;
+		goto use_these_perms;
+	}
+
+	/* use the third 8-bits of permissions for keys the caller has a group
+	 * membership in common with */
+	if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
+		if (gid_eq(key->gid, cred->fsgid)) {
+			kperm = key->perm >> 8;
+			goto use_these_perms;
+		}
+
+		ret = groups_search(cred->group_info, key->gid);
+		if (ret) {
+			kperm = key->perm >> 8;
+			goto use_these_perms;
+		}
+	}
+
+	/* otherwise use the least-significant 8-bits */
+	kperm = key->perm;
+
+use_these_perms:
+
+	/* use the top 8-bits of permissions for keys the caller possesses
+	 * - possessor permissions are additive with other permissions
+	 */
+	if (is_key_possessed(key_ref))
+		kperm |= key->perm >> 24;
+
+	if ((kperm & mask) != mask)
+		return -EACCES;
+
+	/* let LSM be the final arbiter */
+lsm:
+	return security_key_permission(key_ref, cred, need_perm);
+}
+EXPORT_SYMBOL(key_task_permission);
+
+/**
+ * key_validate - Validate a key.
+ * @key: The key to be validated.
+ *
+ * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
+ * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
+ * the key has been revoked or -EKEYEXPIRED if the key has expired.
+ */
+int key_validate(const struct key *key)
+{
+	unsigned long flags = READ_ONCE(key->flags);
+	time64_t expiry = READ_ONCE(key->expiry);
+
+	if (flags & (1 << KEY_FLAG_INVALIDATED))
+		return -ENOKEY;
+
+	/* check it's still accessible */
+	if (flags & ((1 << KEY_FLAG_REVOKED) |
+		     (1 << KEY_FLAG_DEAD)))
+		return -EKEYREVOKED;
+
+	/* check it hasn't expired */
+	if (expiry) {
+		if (ktime_get_real_seconds() >= expiry)
+			return -EKEYEXPIRED;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(key_validate);