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, 58 insertions, 0 deletions

diff --git a/fs/btrfs/ref-verify.h b/fs/btrfs/ref-verify.h
new file mode 100644
index 000000000..1ce544d53
--- /dev/null
+++ b/fs/btrfs/ref-verify.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2014 Facebook.  All rights reserved.
+ */
+
+#ifndef BTRFS_REF_VERIFY_H
+#define BTRFS_REF_VERIFY_H
+
+#include <linux/types.h>
+#include <linux/rbtree_types.h>
+
+struct btrfs_fs_info;
+struct btrfs_ref;
+
+#ifdef CONFIG_BTRFS_DEBUG
+
+#include <linux/spinlock.h>
+
+int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info);
+void btrfs_free_ref_cache(struct btrfs_fs_info *fs_info);
+int btrfs_ref_tree_mod(struct btrfs_fs_info *fs_info,
+		       const struct btrfs_ref *generic_ref);
+void btrfs_free_ref_tree_range(struct btrfs_fs_info *fs_info, u64 start,
+			       u64 len);
+
+static inline void btrfs_init_ref_verify(struct btrfs_fs_info *fs_info)
+{
+	spin_lock_init(&fs_info->ref_verify_lock);
+	fs_info->block_tree = RB_ROOT;
+}
+#else
+static inline int btrfs_build_ref_tree(struct btrfs_fs_info *fs_info)
+{
+	return 0;
+}
+
+static inline void btrfs_free_ref_cache(struct btrfs_fs_info *fs_info)
+{
+}
+
+static inline int btrfs_ref_tree_mod(struct btrfs_fs_info *fs_info,
+				     const struct btrfs_ref *generic_ref)
+{
+	return 0;
+}
+
+static inline void btrfs_free_ref_tree_range(struct btrfs_fs_info *fs_info,
+					     u64 start, u64 len)
+{
+}
+
+static inline void btrfs_init_ref_verify(struct btrfs_fs_info *fs_info)
+{
+}
+
+#endif /* CONFIG_BTRFS_DEBUG */
+
+#endif