From 4a06fa67c4da20148803525151845276cdb995c1 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Mon, 7 Jan 2019 16:47:33 -0500 Subject: 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 Suggested-by: Eric Dumazet Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- net/ipv6/datagram.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'net/ipv6/datagram.c') diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c index bde08aa549f3..c2262a7e2088 100644 --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -700,17 +700,15 @@ void ip6_datagram_recv_specific_ctl(struct sock *sk, struct msghdr *msg, } if (np->rxopt.bits.rxorigdstaddr) { struct sockaddr_in6 sin6; - __be16 *ports; - int end; + __be16 _ports[2], *ports; - end = skb_transport_offset(skb) + 4; - if (end <= 0 || pskb_may_pull(skb, end)) { + ports = skb_header_pointer(skb, skb_transport_offset(skb), + sizeof(_ports), &_ports); + if (ports) { /* 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); - sin6.sin6_family = AF_INET6; sin6.sin6_addr = ipv6_hdr(skb)->daddr; sin6.sin6_port = ports[1]; -- cgit v1.2.3-59-g8ed1b