dccp/tcp: do not inherit mc_list from parent (CVE-2017-8890)

debian/changelog

@@ -412,6 +412,7 @@ linux (4.9.30-1) UNRELEASED; urgency=medium
   [ Salvatore Bonaccorso ]
   * tracing: Use strlcpy() instead of strcpy() in __trace_find_cmdline()
     (CVE-2017-0605)
+  * dccp/tcp: do not inherit mc_list from parent (CVE-2017-8890)
 
  -- Ben Hutchings <ben@decadent.org.uk>  Mon, 08 May 2017 21:11:08 +0200
 

debian/patches/bugfix/all/dccp-tcp-do-not-inherit-mc_list-from-parent.patch

@@ -0,0 +1,42 @@
+From: Eric Dumazet <edumazet@google.com>
+Date: Tue, 9 May 2017 06:29:19 -0700
+Subject: dccp/tcp: do not inherit mc_list from parent
+Origin: https://git.kernel.org/linus/657831ffc38e30092a2d5f03d385d710eb88b09a
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-8890
+
+syzkaller found a way to trigger double frees from ip_mc_drop_socket()
+
+It turns out that leave a copy of parent mc_list at accept() time,
+which is very bad.
+
+Very similar to commit 8b485ce69876 ("tcp: do not inherit
+fastopen_req from parent")
+
+Initial report from Pray3r, completed by Andrey one.
+Thanks a lot to them !
+
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Reported-by: Pray3r <pray3r.z@gmail.com>
+Reported-by: Andrey Konovalov <andreyknvl@google.com>
+Tested-by: Andrey Konovalov <andreyknvl@google.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ net/ipv4/inet_connection_sock.c | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
+index 5e313c1..1054d33 100644
+--- a/net/ipv4/inet_connection_sock.c
++++ b/net/ipv4/inet_connection_sock.c
+@@ -794,6 +794,8 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
+ 		/* listeners have SOCK_RCU_FREE, not the children */
+ 		sock_reset_flag(newsk, SOCK_RCU_FREE);
+ 
++		inet_sk(newsk)->mc_list = NULL;
++
+ 		newsk->sk_mark = inet_rsk(req)->ir_mark;
+ 		atomic64_set(&newsk->sk_cookie,
+ 			     atomic64_read(&inet_rsk(req)->ir_cookie));
+-- 
+2.1.4
+

debian/patches/series

@@ -105,6 +105,7 @@ features/all/securelevel/arm64-add-kernel-config-option-to-set-securelevel-wh.pa
 debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
 debian/time-mark-timer_stats-as-broken.patch
 bugfix/all/tracing-Use-strlcpy-instead-of-strcpy-in-__trace_fin.patch
+bugfix/all/dccp-tcp-do-not-inherit-mc_list-from-parent.patch
 
 # Fix exported symbol versions
 bugfix/ia64/revert-ia64-move-exports-to-definitions.patch