dccp/tcp: do not inherit mc_list from parent

commit 657831ffc38e30092a2d5f03d385d710eb88b09a upstream.

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 907ef2c..a6988e7 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -604,6 +604,8 @@ struct sock *inet_csk_clone(struct sock *sk, const struct request_sock *req,
                inet_sk(newsk)->inet_sport = inet_rsk(req)->loc_port;
                newsk->sk_write_space = sk_stream_write_space;
 
+               inet_sk(newsk)->mc_list = NULL;
+
                newicsk->icsk_retransmits = 0;
                newicsk->icsk_backoff     = 0;
                newicsk->icsk_probes_out  = 0;