dccp: fix freeing skb too early for IPV6_RECVPKTINFO (CVE-2017-6074)

debian/changelog

@@ -41,6 +41,9 @@ linux (4.9.11-1) UNRELEASED; urgency=medium
   * net: Ignore ABI changes to can_rx_register(), ip6_xmit()
   * net: Avoid ABI change for min_header_len
 
+  [ Salvatore Bonaccorso ]
+  * dccp: fix freeing skb too early for IPV6_RECVPKTINFO (CVE-2017-6074)
+
  -- Ben Hutchings <ben@decadent.org.uk>  Sat, 18 Feb 2017 00:38:10 +0000
 
 linux (4.9.10-1) unstable; urgency=medium

debian/patches/bugfix/all/dccp-fix-freeing-skb-too-early-for-IPV6_RECVPKTINFO.patch

@@ -0,0 +1,47 @@
+From: Andrey Konovalov <andreyknvl@google.com>
+Date: Thu, 16 Feb 2017 17:22:46 +0100
+Subject: dccp: fix freeing skb too early for IPV6_RECVPKTINFO
+Origin: https://git.kernel.org/linus/5edabca9d4cff7f1f2b68f0bac55ef99d9798ba4
+
+In the current DCCP implementation an skb for a DCCP_PKT_REQUEST packet
+is forcibly freed via __kfree_skb in dccp_rcv_state_process if
+dccp_v6_conn_request successfully returns.
+
+However, if IPV6_RECVPKTINFO is set on a socket, the address of the skb
+is saved to ireq->pktopts and the ref count for skb is incremented in
+dccp_v6_conn_request, so skb is still in use. Nevertheless, it gets freed
+in dccp_rcv_state_process.
+
+Fix by calling consume_skb instead of doing goto discard and therefore
+calling __kfree_skb.
+
+Similar fixes for TCP:
+
+fb7e2399ec17f1004c0e0ccfd17439f8759ede01 [TCP]: skb is unexpectedly freed.
+0aea76d35c9651d55bbaf746e7914e5f9ae5a25d tcp: SYN packets are now
+simply consumed
+
+Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
+Acked-by: Eric Dumazet <edumazet@google.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/dccp/input.c | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/net/dccp/input.c b/net/dccp/input.c
+index ba34718..8fedc2d 100644
+--- a/net/dccp/input.c
++++ b/net/dccp/input.c
+@@ -606,7 +606,8 @@ int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
+ 			if (inet_csk(sk)->icsk_af_ops->conn_request(sk,
+ 								    skb) < 0)
+ 				return 1;
+-			goto discard;
++			consume_skb(skb);
++			return 0;
+ 		}
+ 		if (dh->dccph_type == DCCP_PKT_RESET)
+ 			goto discard;
+-- 
+2.1.4
+

debian/patches/series

@@ -108,6 +108,7 @@ features/all/securelevel/arm64-add-kernel-config-option-to-set-securelevel-wh.pa
 
 # Security fixes
 debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
+bugfix/all/dccp-fix-freeing-skb-too-early-for-IPV6_RECVPKTINFO.patch
 
 # Fix exported symbol versions
 bugfix/ia64/revert-ia64-move-exports-to-definitions.patch