Commit df20f746 authored Jul 23, 2018 by Willem de Bruijn Committed by Greg Kroah-Hartman Jul 28, 2018

ip: in cmsg IP(V6)_ORIGDSTADDR call pskb_may_pull

[ Upstream commit 2efd4fca703a6707cad16ab486eaab8fc7f0fd49 ]

Syzbot reported a read beyond the end of the skb head when returning
IPV6_ORIGDSTADDR:

  BUG: KMSAN: kernel-infoleak in put_cmsg+0x5ef/0x860 net/core/scm.c:242
  CPU: 0 PID: 4501 Comm: syz-executor128 Not tainted 4.17.0+ #9
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
  Google 01/01/2011
  Call Trace:
    __dump_stack lib/dump_stack.c:77 [inline]
    dump_stack+0x185/0x1d0 lib/dump_stack.c:113
    kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1125
    kmsan_internal_check_memory+0x138/0x1f0 mm/kmsan/kmsan.c:1219
    kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1261
    copy_to_user include/linux/uaccess.h:184 [inline]
    put_cmsg+0x5ef/0x860 net/core/scm.c:242
    ip6_datagram_recv_specific_ctl+0x1cf3/0x1eb0 net/ipv6/datagram.c:719
    ip6_datagram_recv_ctl+0x41c/0x450 net/ipv6/datagram.c:733
    rawv6_recvmsg+0x10fb/0x1460 net/ipv6/raw.c:521
    [..]

This logic and its ipv4 counterpart read the destination port from
the packet at skb_transport_offset(skb) + 4.

With MSG_MORE and a local SOCK_RAW sender, syzbot was able to cook a
packet that stores headers exactly up to skb_transport_offset(skb) in
the head and the remainder in a frag.

Call pskb_may_pull before accessing the pointer to ensure that it lies
in skb head.

Link: http://lkml.kernel.org/r/CAF=yD-LEJwZj5a1-bAAj2Oy_hKmGygV6rsJ_WOrAYnv-fnayiQ@mail.gmail.com


Reported-by:  <syzbot+9adb4b567003cac781f0@syzkaller.appspotmail.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>

parent c2ce657f

net/ipv4/ip_sockglue.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -148,15 +148,18 @@ static void ip_cmsg_recv_dstaddr(struct msghdr msg, struct sk_buff skb)
		{
		struct sockaddr_in sin;
		const struct iphdr *iph = ip_hdr(skb);
		__be16 ports = (__be16 )skb_transport_header(skb);
		__be16 *ports;
		int end;

		if (skb_transport_offset(skb) + 4 > (int)skb->len)
		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);

		sin.sin_family = AF_INET;
		sin.sin_addr.s_addr = iph->daddr;

net/ipv6/datagram.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -708,13 +708,16 @@ void ip6_datagram_recv_specific_ctl(struct sock sk, struct msghdr msg,
		}
		if (np->rxopt.bits.rxorigdstaddr) {
		struct sockaddr_in6 sin6;
		__be16 ports = (__be16 ) skb_transport_header(skb);
		__be16 *ports;
		int end;

		if (skb_transport_offset(skb) + 4 <= (int)skb->len) {
		end = skb_transport_offset(skb) + 4;
		if (end <= 0 \|\| pskb_may_pull(skb, end)) {
		/* 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;