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, 118 insertions, 0 deletions

diff --git a/net/ipv6/rpl.c b/net/ipv6/rpl.c
new file mode 100644
index 000000000..e186998bf
--- /dev/null
+++ b/net/ipv6/rpl.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Authors:
+ * (C) 2020 Alexander Aring <alex.aring@gmail.com>
+ */
+
+#include <net/ipv6.h>
+#include <net/rpl.h>
+
+#define IPV6_PFXTAIL_LEN(x) (sizeof(struct in6_addr) - (x))
+#define IPV6_RPL_BEST_ADDR_COMPRESSION 15
+
+static void ipv6_rpl_addr_decompress(struct in6_addr *dst,
+				     const struct in6_addr *daddr,
+				     const void *post, unsigned char pfx)
+{
+	memcpy(dst, daddr, pfx);
+	memcpy(&dst->s6_addr[pfx], post, IPV6_PFXTAIL_LEN(pfx));
+}
+
+static void ipv6_rpl_addr_compress(void *dst, const struct in6_addr *addr,
+				   unsigned char pfx)
+{
+	memcpy(dst, &addr->s6_addr[pfx], IPV6_PFXTAIL_LEN(pfx));
+}
+
+static void *ipv6_rpl_segdata_pos(const struct ipv6_rpl_sr_hdr *hdr, int i)
+{
+	return (void *)&hdr->rpl_segdata[i * IPV6_PFXTAIL_LEN(hdr->cmpri)];
+}
+
+void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr,
+			     const struct ipv6_rpl_sr_hdr *inhdr,
+			     const struct in6_addr *daddr, unsigned char n)
+{
+	int i;
+
+	outhdr->nexthdr = inhdr->nexthdr;
+	outhdr->hdrlen = (((n + 1) * sizeof(struct in6_addr)) >> 3);
+	outhdr->pad = 0;
+	outhdr->type = inhdr->type;
+	outhdr->segments_left = inhdr->segments_left;
+	outhdr->cmpri = 0;
+	outhdr->cmpre = 0;
+
+	for (i = 0; i < n; i++)
+		ipv6_rpl_addr_decompress(&outhdr->rpl_segaddr[i], daddr,
+					 ipv6_rpl_segdata_pos(inhdr, i),
+					 inhdr->cmpri);
+
+	ipv6_rpl_addr_decompress(&outhdr->rpl_segaddr[n], daddr,
+				 ipv6_rpl_segdata_pos(inhdr, n),
+				 inhdr->cmpre);
+}
+
+static unsigned char ipv6_rpl_srh_calc_cmpri(const struct ipv6_rpl_sr_hdr *inhdr,
+					     const struct in6_addr *daddr,
+					     unsigned char n)
+{
+	unsigned char plen;
+	int i;
+
+	for (plen = 0; plen < sizeof(*daddr); plen++) {
+		for (i = 0; i < n; i++) {
+			if (daddr->s6_addr[plen] !=
+			    inhdr->rpl_segaddr[i].s6_addr[plen])
+				return plen;
+		}
+	}
+
+	return IPV6_RPL_BEST_ADDR_COMPRESSION;
+}
+
+static unsigned char ipv6_rpl_srh_calc_cmpre(const struct in6_addr *daddr,
+					     const struct in6_addr *last_segment)
+{
+	unsigned int plen;
+
+	for (plen = 0; plen < sizeof(*daddr); plen++) {
+		if (daddr->s6_addr[plen] != last_segment->s6_addr[plen])
+			return plen;
+	}
+
+	return IPV6_RPL_BEST_ADDR_COMPRESSION;
+}
+
+void ipv6_rpl_srh_compress(struct ipv6_rpl_sr_hdr *outhdr,
+			   const struct ipv6_rpl_sr_hdr *inhdr,
+			   const struct in6_addr *daddr, unsigned char n)
+{
+	unsigned char cmpri, cmpre;
+	size_t seglen;
+	int i;
+
+	cmpri = ipv6_rpl_srh_calc_cmpri(inhdr, daddr, n);
+	cmpre = ipv6_rpl_srh_calc_cmpre(daddr, &inhdr->rpl_segaddr[n]);
+
+	outhdr->nexthdr = inhdr->nexthdr;
+	seglen = (n * IPV6_PFXTAIL_LEN(cmpri)) + IPV6_PFXTAIL_LEN(cmpre);
+	outhdr->hdrlen = seglen >> 3;
+	if (seglen & 0x7) {
+		outhdr->hdrlen++;
+		outhdr->pad = 8 - (seglen & 0x7);
+	} else {
+		outhdr->pad = 0;
+	}
+	outhdr->type = inhdr->type;
+	outhdr->segments_left = inhdr->segments_left;
+	outhdr->cmpri = cmpri;
+	outhdr->cmpre = cmpre;
+
+	for (i = 0; i < n; i++)
+		ipv6_rpl_addr_compress(ipv6_rpl_segdata_pos(outhdr, i),
+				       &inhdr->rpl_segaddr[i], cmpri);
+
+	ipv6_rpl_addr_compress(ipv6_rpl_segdata_pos(outhdr, n),
+			       &inhdr->rpl_segaddr[n], cmpre);
+}