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/fs_dirent.c b/fs/fs_dirent.c
new file mode 100644
index 000000000..e5e08f213
--- /dev/null
+++ b/fs/fs_dirent.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs_dirent.h>
+#include <linux/export.h>
+
+/*
+ * fs on-disk file type to dirent file type conversion
+ */
+static const unsigned char fs_dtype_by_ftype[FT_MAX] = {
+	[FT_UNKNOWN]	= DT_UNKNOWN,
+	[FT_REG_FILE]	= DT_REG,
+	[FT_DIR]	= DT_DIR,
+	[FT_CHRDEV]	= DT_CHR,
+	[FT_BLKDEV]	= DT_BLK,
+	[FT_FIFO]	= DT_FIFO,
+	[FT_SOCK]	= DT_SOCK,
+	[FT_SYMLINK]	= DT_LNK
+};
+
+/**
+ * fs_ftype_to_dtype() - fs on-disk file type to dirent type.
+ * @filetype: The on-disk file type to convert.
+ *
+ * This function converts the on-disk file type value (FT_*) to the directory
+ * entry type (DT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * DT_UNKNOWN		- Unknown type
+ * * DT_FIFO		- FIFO
+ * * DT_CHR		- Character device
+ * * DT_DIR		- Directory
+ * * DT_BLK		- Block device
+ * * DT_REG		- Regular file
+ * * DT_LNK		- Symbolic link
+ * * DT_SOCK		- Local-domain socket
+ */
+unsigned char fs_ftype_to_dtype(unsigned int filetype)
+{
+	if (filetype >= FT_MAX)
+		return DT_UNKNOWN;
+
+	return fs_dtype_by_ftype[filetype];
+}
+EXPORT_SYMBOL_GPL(fs_ftype_to_dtype);
+
+/*
+ * dirent file type to fs on-disk file type conversion
+ * Values not initialized explicitly are FT_UNKNOWN (0).
+ */
+static const unsigned char fs_ftype_by_dtype[DT_MAX] = {
+	[DT_REG]	= FT_REG_FILE,
+	[DT_DIR]	= FT_DIR,
+	[DT_LNK]	= FT_SYMLINK,
+	[DT_CHR]	= FT_CHRDEV,
+	[DT_BLK]	= FT_BLKDEV,
+	[DT_FIFO]	= FT_FIFO,
+	[DT_SOCK]	= FT_SOCK,
+};
+
+/**
+ * fs_umode_to_ftype() - file mode to on-disk file type.
+ * @mode: The file mode to convert.
+ *
+ * This function converts the file mode value to the on-disk file type (FT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * FT_UNKNOWN		- Unknown type
+ * * FT_REG_FILE	- Regular file
+ * * FT_DIR		- Directory
+ * * FT_CHRDEV		- Character device
+ * * FT_BLKDEV		- Block device
+ * * FT_FIFO		- FIFO
+ * * FT_SOCK		- Local-domain socket
+ * * FT_SYMLINK		- Symbolic link
+ */
+unsigned char fs_umode_to_ftype(umode_t mode)
+{
+	return fs_ftype_by_dtype[S_DT(mode)];
+}
+EXPORT_SYMBOL_GPL(fs_umode_to_ftype);
+
+/**
+ * fs_umode_to_dtype() - file mode to dirent file type.
+ * @mode: The file mode to convert.
+ *
+ * This function converts the file mode value to the directory
+ * entry type (DT_*).
+ *
+ * Context: Any context.
+ * Return:
+ * * DT_UNKNOWN		- Unknown type
+ * * DT_FIFO		- FIFO
+ * * DT_CHR		- Character device
+ * * DT_DIR		- Directory
+ * * DT_BLK		- Block device
+ * * DT_REG		- Regular file
+ * * DT_LNK		- Symbolic link
+ * * DT_SOCK		- Local-domain socket
+ */
+unsigned char fs_umode_to_dtype(umode_t mode)
+{
+	return fs_ftype_to_dtype(fs_umode_to_ftype(mode));
+}
+EXPORT_SYMBOL_GPL(fs_umode_to_dtype);