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, 120 insertions, 0 deletions

diff --git a/fs/efs/namei.c b/fs/efs/namei.c
new file mode 100644
index 000000000..38961ee1d
--- /dev/null
+++ b/fs/efs/namei.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * namei.c
+ *
+ * Copyright (c) 1999 Al Smith
+ *
+ * Portions derived from work (c) 1995,1996 Christian Vogelgsang.
+ */
+
+#include <linux/buffer_head.h>
+#include <linux/string.h>
+#include <linux/exportfs.h>
+#include "efs.h"
+
+
+static efs_ino_t efs_find_entry(struct inode *inode, const char *name, int len)
+{
+	struct buffer_head *bh;
+
+	int			slot, namelen;
+	char			*nameptr;
+	struct efs_dir		*dirblock;
+	struct efs_dentry	*dirslot;
+	efs_ino_t		inodenum;
+	efs_block_t		block;
+ 
+	if (inode->i_size & (EFS_DIRBSIZE-1))
+		pr_warn("%s(): directory size not a multiple of EFS_DIRBSIZE\n",
+			__func__);
+
+	for(block = 0; block < inode->i_blocks; block++) {
+
+		bh = sb_bread(inode->i_sb, efs_bmap(inode, block));
+		if (!bh) {
+			pr_err("%s(): failed to read dir block %d\n",
+			       __func__, block);
+			return 0;
+		}
+    
+		dirblock = (struct efs_dir *) bh->b_data;
+
+		if (be16_to_cpu(dirblock->magic) != EFS_DIRBLK_MAGIC) {
+			pr_err("%s(): invalid directory block\n", __func__);
+			brelse(bh);
+			return 0;
+		}
+
+		for (slot = 0; slot < dirblock->slots; slot++) {
+			dirslot  = (struct efs_dentry *) (((char *) bh->b_data) + EFS_SLOTAT(dirblock, slot));
+
+			namelen  = dirslot->namelen;
+			nameptr  = dirslot->name;
+
+			if ((namelen == len) && (!memcmp(name, nameptr, len))) {
+				inodenum = be32_to_cpu(dirslot->inode);
+				brelse(bh);
+				return inodenum;
+			}
+		}
+		brelse(bh);
+	}
+	return 0;
+}
+
+struct dentry *efs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
+{
+	efs_ino_t inodenum;
+	struct inode *inode = NULL;
+
+	inodenum = efs_find_entry(dir, dentry->d_name.name, dentry->d_name.len);
+	if (inodenum)
+		inode = efs_iget(dir->i_sb, inodenum);
+
+	return d_splice_alias(inode, dentry);
+}
+
+static struct inode *efs_nfs_get_inode(struct super_block *sb, u64 ino,
+		u32 generation)
+{
+	struct inode *inode;
+
+	if (ino == 0)
+		return ERR_PTR(-ESTALE);
+	inode = efs_iget(sb, ino);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	if (generation && inode->i_generation != generation) {
+		iput(inode);
+		return ERR_PTR(-ESTALE);
+	}
+
+	return inode;
+}
+
+struct dentry *efs_fh_to_dentry(struct super_block *sb, struct fid *fid,
+		int fh_len, int fh_type)
+{
+	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
+				    efs_nfs_get_inode);
+}
+
+struct dentry *efs_fh_to_parent(struct super_block *sb, struct fid *fid,
+		int fh_len, int fh_type)
+{
+	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
+				    efs_nfs_get_inode);
+}
+
+struct dentry *efs_get_parent(struct dentry *child)
+{
+	struct dentry *parent = ERR_PTR(-ENOENT);
+	efs_ino_t ino;
+
+	ino = efs_find_entry(d_inode(child), "..", 2);
+	if (ino)
+		parent = d_obtain_alias(efs_iget(child->d_sb, ino));
+
+	return parent;
+}