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, 28 insertions, 0 deletions

diff --git a/fs/befs/Kconfig b/fs/befs/Kconfig
new file mode 100644
index 000000000..5fcfc4024
--- /dev/null
+++ b/fs/befs/Kconfig
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config BEFS_FS
+	tristate "BeOS file system (BeFS) support (read only)"
+	depends on BLOCK
+	select BUFFER_HEAD
+	select NLS
+	help
+	  The BeOS File System (BeFS) is the native file system of Be, Inc's
+	  BeOS. Notable features include support for arbitrary attributes
+	  on files and directories, and database-like indices on selected
+	  attributes. (Also note that this driver doesn't make those features
+	  available at this time). It is a 64 bit filesystem, so it supports
+	  extremely large volumes and files.
+
+	  If you use this filesystem, you should also say Y to at least one
+	  of the NLS (native language support) options below.
+
+	  If you don't know what this is about, say N.
+
+	  To compile this as a module, choose M here: the module will be
+	  called befs.
+
+config BEFS_DEBUG
+	bool "Debug BeFS"
+	depends on BEFS_FS
+	help
+	  If you say Y here, you can use the 'debug' mount option to enable
+	  debugging output from the driver.