[patch net v4] tcp: prohibit TCP_REPAIR_OPTIONS if data was already sent

[patch net v4] tcp: prohibit TCP_REPAIR_OPTIONS if data was already sent

[Lu Wei]

If setsockopt with option name of TCP_REPAIR_OPTIONS and opt_code
of TCPOPT_SACK_PERM is called to enable sack after data is sent
and dupacks are received , it will trigger a warning in function
tcp_verify_left_out() as follows:

============================================
WARNING: CPU: 8 PID: 0 at net/ipv4/tcp_input.c:2132
tcp_timeout_mark_lost+0x154/0x160
tcp_enter_loss+0x2b/0x290
tcp_retransmit_timer+0x50b/0x640
tcp_write_timer_handler+0x1c8/0x340
tcp_write_timer+0xe5/0x140
call_timer_fn+0x3a/0x1b0
__run_timers.part.0+0x1bf/0x2d0
run_timer_softirq+0x43/0xb0
__do_softirq+0xfd/0x373
__irq_exit_rcu+0xf6/0x140

The warning is caused in the following steps:
1. a socket named socketA is created
2. socketA enters repair mode without build a connection
3. socketA calls connect() and its state is changed to TCP_ESTABLISHED
   directly
4. socketA leaves repair mode
5. socketA calls sendmsg() to send data, packets_out and sack_outs(dup
   ack receives) increase
6. socketA enters repair mode again
7. socketA calls setsockopt with TCPOPT_SACK_PERM to enable sack
8. retransmit timer expires, it calls tcp_timeout_mark_lost(), lost_out
   increases
9. sack_outs + lost_out > packets_out triggers since lost_out and
   sack_outs increase repeatly

In function tcp_timeout_mark_lost(), tp->sacked_out will be cleared if
Step7 not happen and the warning will not be triggered. As suggested by
Denis and Eric, TCP_REPAIR_OPTIONS should be prohibited if data was
already sent. So this patch checks tp->segs_out, only TCP_REPAIR_OPTIONS
can be set only if tp->segs_out is 0.

socket-tcp tests in CRIU has been tested as follows:
$ sudo ./test/zdtm.py run -t zdtm/static/socket-tcp*  --keep-going \
       --ignore-taint

socket-tcp* represent all socket-tcp tests in test/zdtm/static/.

Fixes: b139ba4e90dc ("tcp: Repair connection-time negotiated parameters")
Signed-off-by: Lu Wei <luwei32@huawei.com>
---
v4: use tp->bytes_sent instead of tp->segs_out
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ef14efa1fb70..54836a6b81d6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3647,7 +3647,7 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 	case TCP_REPAIR_OPTIONS:
 		if (!tp->repair)
 			err = -EINVAL;
-		else if (sk->sk_state == TCP_ESTABLISHED)
+		else if (sk->sk_state == TCP_ESTABLISHED && !tp->bytes_sent)
 			err = tcp_repair_options_est(sk, optval, optlen);
 		else
 			err = -EPERM;
-- 
2.31.1

Re: [patch net v4] tcp: prohibit TCP_REPAIR_OPTIONS if data was already sent

[Neal Cardwell]

On Thu, Nov 3, 2022 at 7:42 AM Lu Wei <luwei32@huawei.com> wrote:
>
> If setsockopt with option name of TCP_REPAIR_OPTIONS and opt_code
> of TCPOPT_SACK_PERM is called to enable sack after data is sent
> and dupacks are received , it will trigger a warning in function
> tcp_verify_left_out() as follows:
>
> ============================================
> WARNING: CPU: 8 PID: 0 at net/ipv4/tcp_input.c:2132
> tcp_timeout_mark_lost+0x154/0x160
> tcp_enter_loss+0x2b/0x290
> tcp_retransmit_timer+0x50b/0x640
> tcp_write_timer_handler+0x1c8/0x340
> tcp_write_timer+0xe5/0x140
> call_timer_fn+0x3a/0x1b0
> __run_timers.part.0+0x1bf/0x2d0
> run_timer_softirq+0x43/0xb0
> __do_softirq+0xfd/0x373
> __irq_exit_rcu+0xf6/0x140
>
> The warning is caused in the following steps:
> 1. a socket named socketA is created
> 2. socketA enters repair mode without build a connection
> 3. socketA calls connect() and its state is changed to TCP_ESTABLISHED
>    directly
> 4. socketA leaves repair mode
> 5. socketA calls sendmsg() to send data, packets_out and sack_outs(dup
>    ack receives) increase
> 6. socketA enters repair mode again
> 7. socketA calls setsockopt with TCPOPT_SACK_PERM to enable sack
> 8. retransmit timer expires, it calls tcp_timeout_mark_lost(), lost_out
>    increases
> 9. sack_outs + lost_out > packets_out triggers since lost_out and
>    sack_outs increase repeatly
>
> In function tcp_timeout_mark_lost(), tp->sacked_out will be cleared if
> Step7 not happen and the warning will not be triggered. As suggested by
> Denis and Eric, TCP_REPAIR_OPTIONS should be prohibited if data was
> already sent. So this patch checks tp->segs_out, only TCP_REPAIR_OPTIONS
> can be set only if tp->segs_out is 0.

This last sentence mentioning tp->segs_out has not been updated to
match the code. :-) You may want to just omit that sentence, since it
is just restating the patch in English prose, and the previous
sentence already conveys the the intent and high-level functionality
("TCP_REPAIR_OPTIONS should be prohibited if data was already sent").

neal