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dccp/tcp: do not inherit mc_list from parent
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 8b485ce ("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 <>
Reported-by: Pray3r <>
Reported-by: Andrey Konovalov <>
Tested-by: Andrey Konovalov <>
Signed-off-by: David S. Miller <>
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Eric Dumazet authored and davem330 committed May 9, 2017
1 parent e735da5 commit 657831ffc38e30092a2d5f03d385d710eb88b09a
Showing with 2 additions and 0 deletions.
  1. +2 −0 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;

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