ip: on queued skb use skb_header_pointer instead of pskb_may_pull
Commit 2efd4fca703a ("ip: in cmsg IP(V6)_ORIGDSTADDR call
pskb_may_pull") avoided a read beyond the end of the skb linear
segment by calling pskb_may_pull.
That function can trigger a BUG_ON in pskb_expand_head if the skb is
shared, which it is when when peeking. It can also return ENOMEM.
Avoid both by switching to safer skb_header_pointer.
Fixes: 2efd4fca703a ("ip: in cmsg IP(V6)_ORIGDSTADDR call pskb_may_pull")
Reported-by: syzbot <syzkaller@googlegroups.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index fffcc13..82f341e 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -148,19 +148,17 @@ static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
{
+ __be16 _ports[2], *ports;
struct sockaddr_in sin;
- __be16 *ports;
- int end;
-
- end = skb_transport_offset(skb) + 4;
- if (end > 0 && !pskb_may_pull(skb, end))
- return;
/* All current transport protocols have the port numbers in the
* first four bytes of the transport header and this function is
* written with this assumption in mind.
*/
- ports = (__be16 *)skb_transport_header(skb);
+ ports = skb_header_pointer(skb, skb_transport_offset(skb),
+ sizeof(_ports), &_ports);
+ if (!ports)
+ return;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = ip_hdr(skb)->daddr;
