linux-kernel - [PATCH 3.2 178/199] net/dccp: fix use-after-free in dccp_invalid

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Message-ID: <lsq.1489146370.825407354@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:10 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Andrey Konovalov" <andreyknvl@...gle.com>
Subject: [PATCH 3.2 178/199] net/dccp: fix use-after-free in
 dccp_invalid_packet

3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit 648f0c28df282636c0c8a7a19ca3ce5fc80a39c3 ]

pskb_may_pull() can reallocate skb->head, we need to reload dh pointer
in dccp_invalid_packet() or risk use after free.

Bug found by Andrey Konovalov using syzkaller.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/dccp/ipv4.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -730,6 +730,7 @@ int dccp_invalid_packet(struct sk_buff *
 {
 	const struct dccp_hdr *dh;
 	unsigned int cscov;
+	u8 dccph_doff;
 
 	if (skb->pkt_type != PACKET_HOST)
 		return 1;
@@ -751,18 +752,19 @@ int dccp_invalid_packet(struct sk_buff *
 	/*
 	 * If P.Data Offset is too small for packet type, drop packet and return
 	 */
-	if (dh->dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
-		DCCP_WARN("P.Data Offset(%u) too small\n", dh->dccph_doff);
+	dccph_doff = dh->dccph_doff;
+	if (dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
+		DCCP_WARN("P.Data Offset(%u) too small\n", dccph_doff);
 		return 1;
 	}
 	/*
 	 * If P.Data Offset is too too large for packet, drop packet and return
 	 */
-	if (!pskb_may_pull(skb, dh->dccph_doff * sizeof(u32))) {
-		DCCP_WARN("P.Data Offset(%u) too large\n", dh->dccph_doff);
+	if (!pskb_may_pull(skb, dccph_doff * sizeof(u32))) {
+		DCCP_WARN("P.Data Offset(%u) too large\n", dccph_doff);
 		return 1;
 	}
-
+	dh = dccp_hdr(skb);
 	/*
 	 * If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet
 	 * has short sequence numbers), drop packet and return