iperf（v3.18）: error - select failed: Bad file descriptor （UAF in race condition?）

# version
iperf：3.18
kernel： 5.10.0-136.95.0.176.27.oe2203sp1.bclinux.aarch64

# method：
server：
taskset -c 21-30 iperf3 -s -p 21000 -V --timestamps -i 30
client：
for i in {1..1000000}; do taskset -c 21-30 iperf3 -c 152.100.1.156 -u -l $((RANDOM%9000 + 22)) -P 16 -t 60 -i 30 -p 21000 -V --timestamps --bidir; sleep 1; if [ $? -ne 0 ];then echo "$(date) error in mix len test >> iperf3mixerr.log"; fi; done

# appearence

# Remark

We have also conducted extensive testing with the newer release, iperf3 version 3.19.1 over 2000 times（about 70hours）and the error did not​ occur a single time.