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, 69 insertions, 0 deletions

diff --git a/fs/bfs/bfs.h b/fs/bfs/bfs.h
new file mode 100644
index 000000000..b08afe733
--- /dev/null
+++ b/fs/bfs/bfs.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *	fs/bfs/bfs.h
+ *	Copyright (C) 1999-2018 Tigran Aivazian <aivazian.tigran@gmail.com>
+ */
+#ifndef _FS_BFS_BFS_H
+#define _FS_BFS_BFS_H
+
+#include <linux/bfs_fs.h>
+
+/* In theory BFS supports up to 512 inodes, numbered from 2 (for /) up to 513 inclusive.
+   In actual fact, attempting to create the 512th inode (i.e. inode No. 513 or file No. 511)
+   will fail with ENOSPC in bfs_add_entry(): the root directory cannot contain so many entries, counting '..'.
+   So, mkfs.bfs(8) should really limit its -N option to 511 and not 512. For now, we just print a warning
+   if a filesystem is mounted with such "impossible to fill up" number of inodes */
+#define BFS_MAX_LASTI	513
+
+/*
+ * BFS file system in-core superblock info
+ */
+struct bfs_sb_info {
+	unsigned long si_blocks;
+	unsigned long si_freeb;
+	unsigned long si_freei;
+	unsigned long si_lf_eblk;
+	unsigned long si_lasti;
+	DECLARE_BITMAP(si_imap, BFS_MAX_LASTI+1);
+	struct mutex bfs_lock;
+};
+
+/*
+ * BFS file system in-core inode info
+ */
+struct bfs_inode_info {
+	unsigned long i_dsk_ino; /* inode number from the disk, can be 0 */
+	unsigned long i_sblock;
+	unsigned long i_eblock;
+	struct mapping_metadata_bhs i_metadata_bhs;
+	struct inode vfs_inode;
+};
+
+static inline struct bfs_sb_info *BFS_SB(struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
+static inline struct bfs_inode_info *BFS_I(struct inode *inode)
+{
+	return container_of(inode, struct bfs_inode_info, vfs_inode);
+}
+
+
+#define printf(format, args...) \
+	printk(KERN_ERR "BFS-fs: %s(): " format, __func__, ## args)
+
+/* inode.c */
+extern struct inode *bfs_iget(struct super_block *sb, unsigned long ino);
+extern void bfs_dump_imap(const char *, struct super_block *);
+
+/* file.c */
+extern const struct inode_operations bfs_file_inops;
+extern const struct file_operations bfs_file_operations;
+extern const struct address_space_operations bfs_aops;
+
+/* dir.c */
+extern const struct inode_operations bfs_dir_inops;
+extern const struct file_operations bfs_dir_operations;
+
+#endif /* _FS_BFS_BFS_H */