net/dccp: fix use-after-free in dccp_invalid_packet
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>
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index b567c87..edbe59d 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -700,6 +700,7 @@
{
const struct dccp_hdr *dh;
unsigned int cscov;
+ u8 dccph_doff;
if (skb->pkt_type != PACKET_HOST)
return 1;
@@ -721,18 +722,19 @@
/*
* 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