Hi,

we use nginx which load-balances toward our snmptrapd. Everything is working fine if we start nginx with root. We would like to change it so nginx (workers) would start with nginx user. I couldn't make it work, do you have any idea what additional thing can I set/check?

nginx -V
nginx version: nginx/1.12.2
built by gcc 4.8.5 20150623 (Red Hat 4.8.5-16) (GCC)
built with OpenSSL 1.0.2k-fips 26 Jan 2017
TLS SNI support enabled
configure arguments: --prefix=/usr/share/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib64/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --http-client-body-temp-path=/var/lib/nginx/tmp/client_body --http-proxy-temp-path=/var/lib/nginx/tmp/proxy --http-fastcgi-temp-path=/var/lib/nginx/tmp/fastcgi --http-uwsgi-temp-path=/var/lib/nginx/tmp/uwsgi --http-scgi-temp-path=/var/lib/nginx/tmp/scgi --pid-path=/run/nginx.pid --lock-path=/run/lock/subsys/nginx --user=nginx --group=nginx --with-file-aio --with-ipv6 --with-http_auth_request_module --with-http_ssl_module --with-http_v2_module --with-http_realip_module --with-http_addition_module --with-http_xslt_module=dynamic --with-http_image_filter_module=dynamic --with-http_geoip_module=dynamic --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_random_index_module --with-http_secure_link_module --with-http_degradation_module --with-http_slice_module --with-http_stub_status_module --with-http_perl_module=dynamic --with-mail=dynamic --with-mail_ssl_module --with-pcre --with-pcre-jit --with-stream=dynamic --with-stream_ssl_module --with-google_perftools_module --with-debug --with-cc-opt='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -mtune=generic' --with-ld-opt='-Wl,-z,relro -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -Wl,-E'

uname -a
Linux c-1 4.14.62-1.el7.centos.ncir.1.x86_64 #1 SMP Wed Aug 15 04:24:17 EEST 2018 x86_64 x86_64 x86_64 GNU/Linux


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observation 0) with root user (master+workers)
everything works fine, snmptrapd gets the traps

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observation 1)
idea: playing with setcap

config:
* with nginx user (master is root, workers are started with nginx user, so in /etc/nginx/nginx.conf 'user nginx;' line is included)
root 2703077 0.0 0.0 59028 2280 ? Ss 11:34 0:00 nginx: master process /usr/sbin/nginx
nginx 2703078 0.0 0.0 59476 4160 ? S 11:34 0:00 nginx: worker process
nginx 2703079 0.0 0.0 59476 4840 ? S 11:34 0:00 nginx: worker process
nginx 2703080 0.0 0.0 59476 4840 ? S 11:34 0:00 nginx: worker process
... etc.
* upstream port is 162, snmptrapd is listening there
* I've tried both capacities:
setcap cap_net_bind_service=+ep /sbin/nginx
setcap cap_net_admin+ep /sbin/nginx
* /etc/nginx/conf.d/stream/snmptrap.conf
upstream snmptrap_upstream {
#server x.y.z.226:162; #commented out for easier testing
#server x.y.z:227162; #commented out for easier testing
server x.y.z.228:162;
}
server {
listen z.y.z.225:162 udp;
proxy_pass snmptrap_upstream;
proxy_timeout 1s;
proxy_responses 0;
proxy_bind $remote_addr transparent;
error_log /var/log/nginx/snmptrap.log;
}
* also tried out switching off iptables



netstat -ulpn | grep 162
udp 0 0 x.y.z.228:162 0.0.0.0:* 2748327/snmptrapd
udp 0 0 x.y.z.225:162 0.0.0.0:* 2743096/nginx: mast


/var/log/nginx/snmptrap.log:
2018/09/12 11:55:04 [alert] 2739785#0: *23 setsockopt(IP_TRANSPARENT) failed (1: Operation not permitted) while connecting to upstream, udp client: x.y.z.225, server: x.y.z.225:162, upstream: "x.y.z.228:162", bytes from/to client:5/0, bytes from/to upstream:0/0

/var/log/nginx/stream.log: error 500 is coming
2018-09-12T11:55:04+03:00 x.y.z.225 UDP 500 0 5 0.000 "0" "0" "0.000"

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observation 2)
idea: trying an other upstream port (>1024), but still the same:

config:
* with nginx user (master is root, workers are started with nginx user, so in /etc/nginx/nginx.conf 'user nginx;' line is included)
* upstream port is 4162
* /etc/nginx/conf.d/stream/snmptrap.conf
upstream snmptrap_upstream {
#server x.y.z.226:162; #commentedout for easier testing
#server x.y.z:227162; #commented out for easier testing
server x.y.z.228:4162;
}
server {
listen z.y.z.225:162 udp;
proxy_pass snmptrap_upstream;
proxy_timeout 1s;
proxy_responses 0;
proxy_bind $remote_addr transparent;
error_log /var/log/nginx/snmptrap.log;
}
* also tried out switching off iptables


netstat -ulpn | grep 162
udp 0 0 x.y.z.228:4162 0.0.0.0:* 2748327/snmptrapd
udp 0 0 x.y.z.225:162 0.0.0.0:* 2743096/nginx: mast


/var/log/nginx/snmptrap.log:
2018/09/12 11:08:03 [alert] 121472#0: *112642 setsockopt(IP_TRANSPARENT) failed (1: Operation not permitted) while connecting to upstream, udp client: x.y.z.225, server: x.y.z.225:162, upstream: "x.y.z.228:4162", bytes from/to client:5/0, bytes from/to upstream:0/0

/var/log/nginx/stream.log: error 500 is coming
2018-09-12T11:08:03+03:00 x.y.z.225 UDP 500 0 5 0.000 "0" "0" "0.000"


Thanks in advance:
Orsi