[PATCH] BGP: Do not start connect retry timer if connect immediately succeeds

[夏泽]

Hello to the community! I have 2 things to clarify here.

On Fri, Oct 17, 2025 at 9:43 PM Ze Xia <billxia135 at gmail.com> wrote:
>
> +    bgp_start_timer(p, conn->connect_timer, p->cf->connect_retry_time);
>

First, the above line is copied from 3.1.2 code and is inconsistent
with master branch, the p
parameter should be removed in master branch, I'm sorry for this mistake.

The second thing is about how to reproduce the bug. It happens
whenever TCP connect()
succeeds immediately, however it's pretty hard to happen in real life
if it is ever possible.
I tried starting two bird daemons that binds to 127.0.0.1 with
different ports, and strace shows
that connect() returns -1 with EINPROGRESS like this:

connect(12, {sa_family=AF_INET, sin_port=htons(179),
sin_addr=inet_addr("127.0.0.1")}, 32) = -1 EINPROGRESS (Operation now
in progress)

which means that the bug won't be reproduced.

I discovered this bug in a very special use case. I'm running a lot of
bird daemons on a single
physical machine to acquire routing tables for a network, and I'm
trying to replace TCP sockets
with UDS(Unix Domain Socket), by LD_PRELOAD-ing a customized .so, as
in this proxychains project:
https://github.com/haad/proxychains/tree/master
Basically I'm replacing the implementation of connect() function
(along with others) in libc.so with my own one,
so all connect() calls made by bird jumps into my code. Then, UDS
connect()-s can success immediately,
thus I returned 0 to connect() call, representing immediate success,
causing the bug to happen.
The phenomenon is that bird actively tears down BGP connections after
connect retry timeout (around 90s,
default value:120s). I can stably reproduce this.

In my use case, I should fix this by emulating real-world behaviours
of connect(), i.e. returning EINPROGRESS
and inject POLLOUT in later poll(). However, I don't think that bird
should rely on the fact that connect() never
immediately success, thus this patch should be applied.