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, 22 insertions, 0 deletions

diff --git a/net/lapb/Kconfig b/net/lapb/Kconfig
new file mode 100644
index 000000000..da87b47f0
--- /dev/null
+++ b/net/lapb/Kconfig
@@ -0,0 +1,22 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# LAPB Data Link Drive
+#
+
+config LAPB
+	tristate "LAPB Data Link Driver"
+	help
+	  Link Access Procedure, Balanced (LAPB) is the data link layer (i.e.
+	  the lower) part of the X.25 protocol. It offers a reliable
+	  connection service to exchange data frames with one other host, and
+	  it is used to transport higher level protocols (mostly X.25 Packet
+	  Layer, the higher part of X.25, but others are possible as well).
+	  Usually, LAPB is used with specialized X.21 network cards, but Linux
+	  currently supports LAPB only over Ethernet connections. If you want
+	  to use LAPB connections over Ethernet, say Y here and to "LAPB over
+	  Ethernet driver" below. Read
+	  <file:Documentation/networking/lapb-module.rst> for technical
+	  details.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called lapb.  If unsure, say N.