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CVE-2024-36905
Disclosure Date: May 30, 2024 (last updated June 27, 2024)
In the Linux kernel, the following vulnerability has been resolved:
tcp: defer shutdown(SEND_SHUTDOWN) for TCP_SYN_RECV sockets
TCP_SYN_RECV state is really special, it is only used by
cross-syn connections, mostly used by fuzzers.
In the following crash [1], syzbot managed to trigger a divide
by zero in tcp_rcv_space_adjust()
A socket makes the following state transitions,
without ever calling tcp_init_transfer(),
meaning tcp_init_buffer_space() is also not called.
TCP_CLOSE
connect()
TCP_SYN_SENT
TCP_SYN_RECV
shutdown() -> tcp_shutdown(sk, SEND_SHUTDOWN)
TCP_FIN_WAIT1
To fix this issue, change tcp_shutdown() to not
perform a TCP_SYN_RECV -> TCP_FIN_WAIT1 transition,
which makes no sense anyway.
When tcp_rcv_state_process() later changes socket state
from TCP_SYN_RECV to TCP_ESTABLISH, then look at
sk->sk_shutdown to finally enter TCP_FIN_WAIT1 state,
and send a FIN packet from a sane socket state.
This means tcp_send_fin() can now be calle…
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