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, 105 insertions, 0 deletions

diff --git a/fs/efs/dir.c b/fs/efs/dir.c
new file mode 100644
index 000000000..35ad0092c
--- /dev/null
+++ b/fs/efs/dir.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * dir.c
+ *
+ * Copyright (c) 1999 Al Smith
+ */
+
+#include <linux/buffer_head.h>
+#include <linux/filelock.h>
+#include "efs.h"
+
+static int efs_readdir(struct file *, struct dir_context *);
+
+const struct file_operations efs_dir_operations = {
+	.llseek		= generic_file_llseek,
+	.read		= generic_read_dir,
+	.iterate_shared	= efs_readdir,
+	.setlease	= generic_setlease,
+};
+
+const struct inode_operations efs_dir_inode_operations = {
+	.lookup		= efs_lookup,
+};
+
+static int efs_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct inode *inode = file_inode(file);
+	efs_block_t		block;
+	int			slot;
+
+	if (inode->i_size & (EFS_DIRBSIZE-1))
+		pr_warn("%s(): directory size not a multiple of EFS_DIRBSIZE\n",
+			__func__);
+
+	/* work out where this entry can be found */
+	block = ctx->pos >> EFS_DIRBSIZE_BITS;
+
+	/* each block contains at most 256 slots */
+	slot  = ctx->pos & 0xff;
+
+	/* look at all blocks */
+	while (block < inode->i_blocks) {
+		struct efs_dir		*dirblock;
+		struct buffer_head *bh;
+
+		/* read the dir 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);
+			break;
+		}
+
+		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);
+			break;
+		}
+
+		for (; slot < dirblock->slots; slot++) {
+			struct efs_dentry *dirslot;
+			efs_ino_t inodenum;
+			const char *nameptr;
+			int namelen;
+
+			if (dirblock->space[slot] == 0)
+				continue;
+
+			dirslot  = (struct efs_dentry *) (((char *) bh->b_data) + EFS_SLOTAT(dirblock, slot));
+
+			inodenum = be32_to_cpu(dirslot->inode);
+			namelen  = dirslot->namelen;
+			nameptr  = dirslot->name;
+			pr_debug("%s(): block %d slot %d/%d: inode %u, name \"%s\", namelen %u\n",
+				 __func__, block, slot, dirblock->slots-1,
+				 inodenum, nameptr, namelen);
+			if (!namelen)
+				continue;
+			/* found the next entry */
+			ctx->pos = (block << EFS_DIRBSIZE_BITS) | slot;
+
+			/* sanity check */
+			if (nameptr - (char *) dirblock + namelen > EFS_DIRBSIZE) {
+				pr_warn("directory entry %d exceeds directory block\n",
+					slot);
+				continue;
+			}
+
+			/* copy filename and data in dirslot */
+			if (!dir_emit(ctx, nameptr, namelen, inodenum, DT_UNKNOWN)) {
+				brelse(bh);
+				return 0;
+			}
+		}
+		brelse(bh);
+
+		slot = 0;
+		block++;
+	}
+	ctx->pos = (block << EFS_DIRBSIZE_BITS) | slot;
+	return 0;
+}