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, 53 insertions, 0 deletions

diff --git a/include/net/dsfield.h b/include/net/dsfield.h
new file mode 100644
index 000000000..a59a57ffc
--- /dev/null
+++ b/include/net/dsfield.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* include/net/dsfield.h - Manipulation of the Differentiated Services field */
+
+/* Written 1998-2000 by Werner Almesberger, EPFL ICA */
+
+
+#ifndef __NET_DSFIELD_H
+#define __NET_DSFIELD_H
+
+#include <linux/types.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <asm/byteorder.h>
+
+
+static inline __u8 ipv4_get_dsfield(const struct iphdr *iph)
+{
+	return iph->tos;
+}
+
+
+static inline __u8 ipv6_get_dsfield(const struct ipv6hdr *ipv6h)
+{
+	return ntohs(*(__force const __be16 *)ipv6h) >> 4;
+}
+
+
+static inline void ipv4_change_dsfield(struct iphdr *iph,__u8 mask,
+    __u8 value)
+{
+        __u32 check = ntohs((__force __be16)iph->check);
+	__u8 dsfield;
+
+	dsfield = (iph->tos & mask) | value;
+	check += iph->tos;
+	if ((check+1) >> 16) check = (check+1) & 0xffff;
+	check -= dsfield;
+	check += check >> 16; /* adjust carry */
+	iph->check = (__force __sum16)htons(check);
+	iph->tos = dsfield;
+}
+
+
+static inline void ipv6_change_dsfield(struct ipv6hdr *ipv6h,__u8 mask,
+    __u8 value)
+{
+	__be16 *p = (__force __be16 *)ipv6h;
+
+	*p = (*p & htons((((u16)mask << 4) | 0xf00f))) | htons((u16)value << 4);
+}
+
+
+#endif