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ipv4: tcp: send zero IPID for RST and ACK sent in SYN-RECV and TIME-WAIT state
[ Upstream commit 431280eebe
]
tcp uses per-cpu (and per namespace) sockets (net->ipv4.tcp_sk) internally
to send some control packets.
1) RST packets, through tcp_v4_send_reset()
2) ACK packets in SYN-RECV and TIME-WAIT state, through tcp_v4_send_ack()
These packets assert IP_DF, and also use the hashed IP ident generator
to provide an IPv4 ID number.
Geoff Alexander reported this could be used to build off-path attacks.
These packets should not be fragmented, since their size is smaller than
IPV4_MIN_MTU. Only some tunneled paths could eventually have to fragment,
regardless of inner IPID.
We really can use zero IPID, to address the flaw, and as a bonus,
avoid a couple of atomic operations in ip_idents_reserve()
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Geoff Alexander <alexandg@cs.unm.edu>
Tested-by: Geoff Alexander <alexandg@cs.unm.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 6 additions and 0 deletions
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@ -2468,6 +2468,12 @@ static int __net_init tcp_sk_init(struct net *net)
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if (res)
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goto fail;
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sock_set_flag(sk, SOCK_USE_WRITE_QUEUE);
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/* Please enforce IP_DF and IPID==0 for RST and
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* ACK sent in SYN-RECV and TIME-WAIT state.
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*/
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inet_sk(sk)->pmtudisc = IP_PMTUDISC_DO;
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*per_cpu_ptr(net->ipv4.tcp_sk, cpu) = sk;
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}
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