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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>
This commit is contained in:
Eric Dumazet 2016-11-28 06:26:49 -08:00 committed by David S. Miller
parent ffac0e967f
commit 648f0c28df
1 changed files with 7 additions and 5 deletions
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12
net/dccp/ipv4.c
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@ -700,6 +700,7 @@ int dccp_invalid_packet(struct sk_buff *skb)
{ {
const struct dccp_hdr *dh; const struct dccp_hdr *dh;
unsigned int cscov; unsigned int cscov;
u8 dccph_doff;
if (skb->pkt_type != PACKET_HOST) if (skb->pkt_type != PACKET_HOST)
return 1; return 1;
@ -721,18 +722,19 @@ int dccp_invalid_packet(struct sk_buff *skb)
/* /*
* If P.Data Offset is too small for packet type, drop packet and return * If P.Data Offset is too small for packet type, drop packet and return
*/ */
if (dh->dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) { dccph_doff = dh->dccph_doff;
DCCP_WARN("P.Data Offset(%u) too small\n", 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; return 1;
} }
/* /*
* If P.Data Offset is too too large for packet, drop packet and return * If P.Data Offset is too too large for packet, drop packet and return
*/ */
if (!pskb_may_pull(skb, dh->dccph_doff * sizeof(u32))) { if (!pskb_may_pull(skb, dccph_doff * sizeof(u32))) {
DCCP_WARN("P.Data Offset(%u) too large\n", dh->dccph_doff); DCCP_WARN("P.Data Offset(%u) too large\n", dccph_doff);
return 1; return 1;
} }
dh = dccp_hdr(skb);
/* /*
* If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet * If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet
* has short sequence numbers), drop packet and return * has short sequence numbers), drop packet and return