netdev - [PATCH] xfrm: Fix wraparound in xfrm_policy_addr

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Date:   Tue, 29 Dec 2020 14:58:06 +0000
From:   Visa Hankala <visa@...kala.org>
To:     Florian Westphal <fw@...len.de>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: [PATCH] xfrm: Fix wraparound in xfrm_policy_addr_delta()

Use three-way comparison for address elements to avoid integer
wraparound in the result of xfrm_policy_addr_delta().

This ensures that the search trees are built and traversed correctly
when the difference between compared address elements is larger
than INT_MAX.

Fixes: 9cf545ebd591d ("xfrm: policy: store inexact policies in a tree ordered by destination address")
Signed-off-by: Visa Hankala <visa@...kala.org>

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index d622c2548d22..d74902f11dde 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -793,15 +793,20 @@ static int xfrm_policy_addr_delta(const xfrm_address_t *a,
 				  const xfrm_address_t *b,
 				  u8 prefixlen, u16 family)
 {
+	u32 ma, mb, mask;
 	unsigned int pdw, pbi;
 	int delta = 0;
 
 	switch (family) {
 	case AF_INET:
-		if (sizeof(long) == 4 && prefixlen == 0)
-			return ntohl(a->a4) - ntohl(b->a4);
-		return (ntohl(a->a4) & ((~0UL << (32 - prefixlen)))) -
-		       (ntohl(b->a4) & ((~0UL << (32 - prefixlen))));
+		mask = ~0U << (32 - prefixlen);
+		ma = ntohl(a->a4) & mask;
+		mb = ntohl(b->a4) & mask;
+		if (ma < mb)
+			delta = -1;
+		else if (ma > mb)
+			delta = 1;
+		break;
 	case AF_INET6:
 		pdw = prefixlen >> 5;
 		pbi = prefixlen & 0x1f;
@@ -812,10 +817,13 @@ static int xfrm_policy_addr_delta(const xfrm_address_t *a,
 				return delta;
 		}
 		if (pbi) {
-			u32 mask = ~0u << (32 - pbi);
-
-			delta = (ntohl(a->a6[pdw]) & mask) -
-				(ntohl(b->a6[pdw]) & mask);
+			mask = ~0U << (32 - pbi);
+			ma = ntohl(a->a6[pdw]) & mask;
+			mb = ntohl(b->a6[pdw]) & mask;
+			if (ma < mb)
+				delta = -1;
+			else if (ma > mb)
+				delta = 1;
 		}
 		break;
 	default:
asd