Wrong permissions cause segfault syslog-ng (with TLS configuration)/ error handling

[Branislav Staron]

System: Ubuntu 14.04 Trusty
Package syslog-ng-core, Version: 3.5.3-1, Arch: amd64 (maybe all)

After sending TLS request (syslog-ng TLS client, Cisco syslog SSL/TLS client, openssl s_client) child process crashes with kernel message:

[155599.792614] syslog-ng[9124]: segfault at 4 ip 00007f5b978f6544 sp 00007fff7a702be8 error 4 in libsyslog-ng-3.5.3.so[7f5b978af000+7e000]
[155602.728656] syslog-ng[10006]: segfault at 4 ip 00007f5b978f6544 sp 00007fff7a702be8 error 4 in libsyslog-ng-3.5.3.so[7f5b978af000+7e000]
[155604.200793] syslog-ng[10011]: segfault at 4 ip 00007f5b978f6544 sp 00007fff7a702be8 error 4 in libsyslog-ng-3.5.3.so[7f5b978af000+7e000]

This problem occurs when a file server.key or server.cer (in config file syslog-ng.conf) has file permissions (perm: 0400, owner/group: non-root ):
-----------------------------------------------------------
dr-x------. root root .
drwxr-xr-x. root root ..
-r--------. 1000 1000 server.cer
-r--------. root root server.key
-----------------------------------------------------------

config file of server (/etc/syslog-ng/syslog-ng.conf)
---------------------------START---------------------------
@version: 3.5
@include "scl.conf"
@include "`scl-root`/system/tty10.conf"

# First, set some global options.
options {
    flush_lines (0);
    time_reopen (10);
    chain_hostnames (off);
    use_dns (no);
    use_fqdn (no);
    create_dirs (yes);
    keep_hostname (no);
    owner("root");
    group("adm");
    perm(0640);
    stats_freq(1);
};

#TCP_TLS
source tls_net {
    tcp(ip(0.0.0.0) port(6514)
       tls(key-file("/etc/syslog-ng/ssl/server.key")
           cert-file("/etc/syslog-ng/ssl/server.cer")
           peer-verify(optional-untrusted)));
};

destination d_net {
    file("/var/log/HOSTS/$FULLHOST/$YEAR/$MONTH/$DAY/$FACILITY-$LEVEL.log"
    owner(root) group(root) perm(0600) dir_perm(0700) create_dirs(yes)
    template ("$DATE $FULLHOST $PROGRAM $TAG [$FACILITY.$LEVEL] $MSG\n") );
};

log { source(tls_net); destination(d_net); };
---------------------------END---------------------------

Reproduce the problem:
-----------------------------------------------------------
- create config file (see above)
- create x509 key pair (server.key, server.cer)
    - set permision - chmod 400 /etc/syslog-ng/ssl/server.*
    - set owner/group (for example): chown 1000:1000 /etc/syslog-ng/ssl/server.cer
- start service syslog-ng
- send TLS request: openssl s_client -connect localhost:6514
- see kernel log (segfault) and log file (no error found in the log files)