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, 102 insertions, 0 deletions

diff --git a/net/atm/atm_misc.c b/net/atm/atm_misc.c
new file mode 100644
index 000000000..a30b83c1c
--- /dev/null
+++ b/net/atm/atm_misc.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+/* net/atm/atm_misc.c - Various functions for use by ATM drivers */
+
+/* Written 1995-2000 by Werner Almesberger, EPFL ICA */
+
+#include <linux/module.h>
+#include <linux/atm.h>
+#include <linux/atmdev.h>
+#include <linux/skbuff.h>
+#include <linux/sonet.h>
+#include <linux/bitops.h>
+#include <linux/errno.h>
+#include <linux/atomic.h>
+
+int atm_charge(struct atm_vcc *vcc, int truesize)
+{
+	atm_force_charge(vcc, truesize);
+	if (atomic_read(&sk_atm(vcc)->sk_rmem_alloc) <= sk_atm(vcc)->sk_rcvbuf)
+		return 1;
+	atm_return(vcc, truesize);
+	atomic_inc(&vcc->stats->rx_drop);
+	return 0;
+}
+EXPORT_SYMBOL(atm_charge);
+
+struct sk_buff *atm_alloc_charge(struct atm_vcc *vcc, int pdu_size,
+				 gfp_t gfp_flags)
+{
+	struct sock *sk = sk_atm(vcc);
+	int guess = SKB_TRUESIZE(pdu_size);
+
+	atm_force_charge(vcc, guess);
+	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) {
+		struct sk_buff *skb = alloc_skb(pdu_size, gfp_flags);
+
+		if (skb) {
+			atomic_add(skb->truesize-guess,
+				   &sk->sk_rmem_alloc);
+			return skb;
+		}
+	}
+	atm_return(vcc, guess);
+	atomic_inc(&vcc->stats->rx_drop);
+	return NULL;
+}
+EXPORT_SYMBOL(atm_alloc_charge);
+
+
+/*
+ * atm_pcr_goal returns the positive PCR if it should be rounded up, the
+ * negative PCR if it should be rounded down, and zero if the maximum available
+ * bandwidth should be used.
+ *
+ * The rules are as follows (* = maximum, - = absent (0), x = value "x",
+ * (x+ = x or next value above x, x- = x or next value below):
+ *
+ *	min max pcr	result		min max pcr	result
+ *	-   -   -	* (UBR only)	x   -   -	x+
+ *	-   -   *	*		x   -   *	*
+ *	-   -   z	z-		x   -   z	z-
+ *	-   *   -	*		x   *   -	x+
+ *	-   *   *	*		x   *   *	*
+ *	-   *   z	z-		x   *   z	z-
+ *	-   y   -	y-		x   y   -	x+
+ *	-   y   *	y-		x   y   *	y-
+ *	-   y   z	z-		x   y   z	z-
+ *
+ * All non-error cases can be converted with the following simple set of rules:
+ *
+ *   if pcr == z then z-
+ *   else if min == x && pcr == - then x+
+ *     else if max == y then y-
+ *	 else *
+ */
+
+int atm_pcr_goal(const struct atm_trafprm *tp)
+{
+	if (tp->pcr && tp->pcr != ATM_MAX_PCR)
+		return -tp->pcr;
+	if (tp->min_pcr && !tp->pcr)
+		return tp->min_pcr;
+	if (tp->max_pcr != ATM_MAX_PCR)
+		return -tp->max_pcr;
+	return 0;
+}
+EXPORT_SYMBOL(atm_pcr_goal);
+
+void sonet_copy_stats(struct k_sonet_stats *from, struct sonet_stats *to)
+{
+#define __HANDLE_ITEM(i) to->i = atomic_read(&from->i)
+	__SONET_ITEMS
+#undef __HANDLE_ITEM
+}
+EXPORT_SYMBOL(sonet_copy_stats);
+
+void sonet_subtract_stats(struct k_sonet_stats *from, struct sonet_stats *to)
+{
+#define __HANDLE_ITEM(i) atomic_sub(to->i, &from->i)
+	__SONET_ITEMS
+#undef __HANDLE_ITEM
+}
+EXPORT_SYMBOL(sonet_subtract_stats);