netdev - [PATCH 14/18] ipv4: prevent bounds-check bypass via speculative execution

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Date:   Fri, 05 Jan 2018 17:11:10 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>, tglx@...utronix.de,
        torvalds@...ux-foundation.org,
        "David S. Miller" <davem@...emloft.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        alan@...ux.intel.com
Subject: [PATCH 14/18] ipv4: prevent bounds-check bypass via speculative
 execution

Static analysis reports that 'offset' may be a user controlled value
that is used as a data dependency reading from a raw_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@...emloft.net>
Cc: Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Cc: netdev@...r.kernel.org
Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 net/ipv4/raw.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 125c1eab3eaa..f72b20131a15 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -57,6 +57,7 @@
 #include <linux/in_route.h>
 #include <linux/route.h>
 #include <linux/skbuff.h>
+#include <linux/compiler.h>
 #include <linux/igmp.h>
 #include <net/net_namespace.h>
 #include <net/dst.h>
@@ -472,17 +473,17 @@ static int raw_getfrag(void *from, char *to, int offset, int len, int odd,
 		       struct sk_buff *skb)
 {
 	struct raw_frag_vec *rfv = from;
+	char *rfv_buf;
 
-	if (offset < rfv->hlen) {
+	if ((rfv_buf = nospec_array_ptr(rfv->hdr.c, offset, rfv->hlen))) {
 		int copy = min(rfv->hlen - offset, len);
 
 		if (skb->ip_summed == CHECKSUM_PARTIAL)
-			memcpy(to, rfv->hdr.c + offset, copy);
+			memcpy(to, rfv_buf, copy);
 		else
 			skb->csum = csum_block_add(
 				skb->csum,
-				csum_partial_copy_nocheck(rfv->hdr.c + offset,
-							  to, copy, 0),
+				csum_partial_copy_nocheck(rfv_buf, to, copy, 0),
 				odd);
 
 		odd = 0;