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, 199 insertions, 0 deletions

diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
new file mode 100644
index 000000000..5f9c05fb1
--- /dev/null
+++ b/fs/sysfs/symlink.c
@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/sysfs/symlink.c - sysfs symlink implementation
+ *
+ * Copyright (c) 2001-3 Patrick Mochel
+ * Copyright (c) 2007 SUSE Linux Products GmbH
+ * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
+ *
+ * Please see Documentation/filesystems/sysfs.rst for more information.
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/kobject.h>
+#include <linux/mutex.h>
+#include <linux/security.h>
+
+#include "sysfs.h"
+
+static int sysfs_do_create_link_sd(struct kernfs_node *parent,
+				   struct kobject *target_kobj,
+				   const char *name, int warn)
+{
+	struct kernfs_node *kn, *target = NULL;
+
+	if (WARN_ON(!name || !parent))
+		return -EINVAL;
+
+	/*
+	 * We don't own @target_kobj and it may be removed at any time.
+	 * Synchronize using sysfs_symlink_target_lock.  See
+	 * sysfs_remove_dir() for details.
+	 */
+	spin_lock(&sysfs_symlink_target_lock);
+	if (target_kobj->sd) {
+		target = target_kobj->sd;
+		kernfs_get(target);
+	}
+	spin_unlock(&sysfs_symlink_target_lock);
+
+	if (!target)
+		return -ENOENT;
+
+	kn = kernfs_create_link(parent, name, target);
+	kernfs_put(target);
+
+	if (!IS_ERR(kn))
+		return 0;
+
+	if (warn && PTR_ERR(kn) == -EEXIST)
+		sysfs_warn_dup(parent, name);
+	return PTR_ERR(kn);
+}
+
+/**
+ *	sysfs_create_link_sd - create symlink to a given object.
+ *	@kn:		directory we're creating the link in.
+ *	@target:	object we're pointing to.
+ *	@name:		name of the symlink.
+ */
+int sysfs_create_link_sd(struct kernfs_node *kn, struct kobject *target,
+			 const char *name)
+{
+	return sysfs_do_create_link_sd(kn, target, name, 1);
+}
+
+static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
+				const char *name, int warn)
+{
+	struct kernfs_node *parent = NULL;
+
+	if (!kobj)
+		parent = sysfs_root_kn;
+	else
+		parent = kobj->sd;
+
+	if (!parent)
+		return -EFAULT;
+
+	return sysfs_do_create_link_sd(parent, target, name, warn);
+}
+
+/**
+ *	sysfs_create_link - create symlink between two objects.
+ *	@kobj:	object whose directory we're creating the link in.
+ *	@target:	object we're pointing to.
+ *	@name:		name of the symlink.
+ */
+int sysfs_create_link(struct kobject *kobj, struct kobject *target,
+		      const char *name)
+{
+	return sysfs_do_create_link(kobj, target, name, 1);
+}
+EXPORT_SYMBOL_GPL(sysfs_create_link);
+
+/**
+ *	sysfs_create_link_nowarn - create symlink between two objects.
+ *	@kobj:	object whose directory we're creating the link in.
+ *	@target:	object we're pointing to.
+ *	@name:		name of the symlink.
+ *
+ *	This function does the same as sysfs_create_link(), but it
+ *	doesn't warn if the link already exists.
+ */
+int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
+			     const char *name)
+{
+	return sysfs_do_create_link(kobj, target, name, 0);
+}
+EXPORT_SYMBOL_GPL(sysfs_create_link_nowarn);
+
+/**
+ *	sysfs_delete_link - remove symlink in object's directory.
+ *	@kobj:	object we're acting for.
+ *	@targ:	object we're pointing to.
+ *	@name:	name of the symlink to remove.
+ *
+ *	Unlike sysfs_remove_link sysfs_delete_link has enough information
+ *	to successfully delete symlinks in tagged directories.
+ */
+void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
+			const char *name)
+{
+	const struct ns_common *ns = NULL;
+
+	/*
+	 * We don't own @target and it may be removed at any time.
+	 * Synchronize using sysfs_symlink_target_lock.  See
+	 * sysfs_remove_dir() for details.
+	 */
+	spin_lock(&sysfs_symlink_target_lock);
+	if (targ->sd && kernfs_ns_enabled(kobj->sd))
+		ns = targ->sd->ns;
+	spin_unlock(&sysfs_symlink_target_lock);
+	kernfs_remove_by_name_ns(kobj->sd, name, ns);
+}
+
+/**
+ *	sysfs_remove_link - remove symlink in object's directory.
+ *	@kobj:	object we're acting for.
+ *	@name:	name of the symlink to remove.
+ */
+void sysfs_remove_link(struct kobject *kobj, const char *name)
+{
+	struct kernfs_node *parent = NULL;
+
+	if (!kobj)
+		parent = sysfs_root_kn;
+	else
+		parent = kobj->sd;
+
+	kernfs_remove_by_name(parent, name);
+}
+EXPORT_SYMBOL_GPL(sysfs_remove_link);
+
+/**
+ *	sysfs_rename_link_ns - rename symlink in object's directory.
+ *	@kobj:	object we're acting for.
+ *	@targ:	object we're pointing to.
+ *	@old:	previous name of the symlink.
+ *	@new:	new name of the symlink.
+ *	@new_ns: new namespace of the symlink.
+ *
+ *	A helper function for the common rename symlink idiom.
+ */
+int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ,
+			 const char *old, const char *new,
+			 const struct ns_common *new_ns)
+{
+	struct kernfs_node *parent, *kn = NULL;
+	const struct ns_common *old_ns = NULL;
+	int result;
+
+	if (!kobj)
+		parent = sysfs_root_kn;
+	else
+		parent = kobj->sd;
+
+	if (targ->sd)
+		old_ns = targ->sd->ns;
+
+	result = -ENOENT;
+	kn = kernfs_find_and_get_ns(parent, old, old_ns);
+	if (!kn)
+		goto out;
+
+	result = -EINVAL;
+	if (kernfs_type(kn) != KERNFS_LINK)
+		goto out;
+	if (kn->symlink.target_kn->priv != targ)
+		goto out;
+
+	result = kernfs_rename_ns(kn, parent, new, new_ns);
+
+out:
+	kernfs_put(kn);
+	return result;
+}
+EXPORT_SYMBOL_GPL(sysfs_rename_link_ns);