ip: on queued skb use skb_header_pointer instead of pskb_may_pull
[ Upstream commit 4a06fa67c4da20148803525151845276cdb995c1 ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 7071ec6..956af11 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -695,17 +695,15 @@
}
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];