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, 42 insertions, 0 deletions

diff --git a/fs/efs/file.c b/fs/efs/file.c
new file mode 100644
index 000000000..9153dfe79
--- /dev/null
+++ b/fs/efs/file.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * file.c
+ *
+ * Copyright (c) 1999 Al Smith
+ *
+ * Portions derived from work (c) 1995,1996 Christian Vogelgsang.
+ */
+
+#include <linux/buffer_head.h>
+#include "efs.h"
+
+int efs_get_block(struct inode *inode, sector_t iblock,
+		  struct buffer_head *bh_result, int create)
+{
+	int error = -EROFS;
+	long phys;
+
+	if (create)
+		return error;
+	if (iblock >= inode->i_blocks)
+		return 0;
+
+	phys = efs_map_block(inode, iblock);
+	if (phys)
+		map_bh(bh_result, inode->i_sb, phys);
+	return 0;
+}
+
+int efs_bmap(struct inode *inode, efs_block_t block) {
+
+	if (block < 0) {
+		pr_warn("%s(): block < 0\n", __func__);
+		return 0;
+	}
+
+	/* are we about to read past the end of a file ? */
+	if (!(block < inode->i_blocks))
+		return 0;
+
+	return efs_map_block(inode, block);
+}