[PATCH 3.16 342/370] net/dccp: fix use-after-free in dccp_invalid_packet

Ben Hutchings
2017-03-10T13:19:59Z

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

--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -743,6 +743,7 @@ 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;
@@ -764,18 +765,19 @@ 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