[PATCH 13/18] ipv6: prevent bounds-check bypass via speculative execution

[Dan Williams]

Static analysis reports that 'offset' may be a user controlled value
that is used as a data dependency reading from a raw6_frag_vec buffer.
In order to avoid potential leaks of kernel memory values, block
speculative execution of the instruction stream that could issue further
reads based on an invalid '*(rfv->c + offset)' value.

Based on an original patch by Elena Reshetova.

Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 net/ipv6/raw.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 761a473a07c5..384e3d59d148 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -33,6 +33,7 @@
 #include <linux/skbuff.h>
 #include <linux/compat.h>
 #include <linux/uaccess.h>
+#include <linux/compiler.h>
 #include <asm/ioctls.h>
 
 #include <net/net_namespace.h>
@@ -725,17 +726,17 @@ static int raw6_getfrag(void *from, char *to, int offset, int len, int odd,
 		       struct sk_buff *skb)
 {
 	struct raw6_frag_vec *rfv = from;
+	char *rfv_buf;
 
-	if (offset < rfv->hlen) {
+	if ((rfv_buf = nospec_array_ptr(rfv->c, offset, rfv->hlen))) {
 		int copy = min(rfv->hlen - offset, len);
 
 		if (skb->ip_summed == CHECKSUM_PARTIAL)
-			memcpy(to, rfv->c + offset, copy);
+			memcpy(to, rfv_buf, copy);
 		else
 			skb->csum = csum_block_add(
 				skb->csum,
-				csum_partial_copy_nocheck(rfv->c + offset,
-							  to, copy, 0),
+				csum_partial_copy_nocheck(rfv_buf, to, copy, 0),
 				odd);
 
 		odd = 0;