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 called from BH
context, and must use GFP_ATOMIC allocations.
[1]
divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 1 PID: 5084 Comm: syz-executor358 Not tainted 6.9.0-rc6-syzkaller-00022-g98369dccd2f8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
RIP: 0010:tcp_rcv_space_adjust+0x2df/0x890 net/ipv4/tcp_input.c:767
Code: e3 04 4c 01 eb 48 8b 44 24 38 0f b6 04 10 84 c0 49 89 d5 0f 85 a5 03 00 00 41 8b 8e c8 09 00 00 89 e8 29 c8 48 0f af c3 31 d2 <48> f7 f1 48 8d 1c 43 49 8d 96 76 08 00 00 48 89 d0 48 c1 e8 03 48
RSP: 0018:ffffc900031ef3f0 EFLAGS: 00010246
RAX: 0c677a10441f8f42 RBX: 000000004fb95e7e RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000027d4b11f R08: ffffffff89e535a4 R09: 1ffffffff25e6ab7
R10: dffffc0000000000 R11: ffffffff8135e920 R12: ffff88802a9f8d30
R13: dffffc0000000000 R14: ffff88802a9f8d00 R15: 1ffff1100553f2da
FS: 00005555775c0380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1155bf2304 CR3: 000000002b9f2000 CR4: 0000000000350ef0
Call Trace:
With Rapid7 live dashboards, I have a clear view of all the assets on my network, which ones can be exploited, and what I need to do in order to reduce the risk in my environment in real-time. No other tool gives us that kind of value and insight.
– Scott Cheney, Manager of Information Security, Sierra View Medical Center