[Proftpd-user] aborting unclosed fiile handle - DB connection reset

Hi all

We recently get a lot of error messages with SFTP stating “aborting 1 unclosed file handle” in the logfile:

2017-10-19 12:40:02,849 mod_sftp/0.9.9[18592]: sending acceptable userauth methods: publickey,password
2017-10-19 12:40:02,867 mod_sftp/0.9.9[18592]: no supplemental groups found for user ’testuser'
2017-10-19 12:40:02,867 mod_sftp/0.9.9[18592]: sending userauth success
2017-10-19 12:40:02,867 mod_sftp/0.9.9[18592]: user 'testuser' authenticated via 'password' method
2017-10-19 12:40:02,882 mod_sftp/0.9.9[18592]: 'subsystem' channel request for 'sftp' subsystem
2017-10-19 12:40:02,883 mod_sftp/0.9.9[18592]: client requested SFTP protocol version 4, which exceeds SFTPClientMatch max SFTP protocol version 3, using protocol version 3
2017-10-19 12:40:02,883 mod_sftp/0.9.9[18592]: using SFTP protocol version 3 for this session (channel ID 1)
2017-10-19 12:40:02,883 mod_sftp/0.9.9[18592]: empty path given in REALPATH request, using '/'
2017-10-19 12:40:02,884 mod_sftp/0.9.9[18592]: 'subsystem' channel request for 'sftp' subsystem
2017-10-19 12:40:02,885 mod_sftp/0.9.9[18592]: client requested SFTP protocol version 4, which exceeds SFTPClientMatch max SFTP protocol version 3, using protocol version 3
2017-10-19 12:40:02,885 mod_sftp/0.9.9[18592]: using SFTP protocol version 3 for this session (channel ID 0)
2017-10-19 12:40:02,925 mod_sftp/0.9.9[18592]: client at 192.168.30.6 sent SSH_DISCONNECT message: The user disconnected the application (Application error)
2017-10-19 12:40:02,927 mod_sftp/0.9.9[18592]: aborting 1 unclosed file handle

The server is configured to only provide SFTP protocol version 1-3 support. Users are stored in a postgresql database where we see a lot of matching errors about connections being reset from the client side with “could not receive data from client: Connection reset by peer”.

It seems that the unclosed file handle message correlates with the database connection being reset without proper handshaking. The sql trace log shows no errors or warnings at all.
Is there any way to debug this further? 

Cheers
-ok


proftpd -V

Compile-time Settings:
  Version: 1.3.5e (maint)
  Platform: LINUX [Linux 3.13.0-100-generic x86_64]
  Built: Wed Oct 4 2017 17:10:28 CEST
  Built With:
    configure  '--prefix=/opt/cargo' '--enable-auth-pam=no' '--disable-ident' '--enable-facl' '--enable-cap' '--enable-nls' '--enable-shared=no' '--enable-static=yes' '--enable-dso=no' '--enable-openssl' '--enable-ctrls' '--enable-timeout-idle=300' '--enable-timeout-stalled=1800' '--enable-pcre' '--with-modules=mod_charset:mod_sql:mod_sftp_sql:mod_sftp:mod_sql_postgres:mod_quotatab:mod_quotatab_sql:mod_unique_id:mod_tls:mod_wrap2:mod_wrap2_sql:mod_sql_passwd:mod_ctrls_admin:mod_ban:mod_clamav:mod_diskuse:mod_exec:mod_deflate:mod_snmp:mod_copy:mod_geoip:mod_ifsession' 'CC=cc' 'CFLAGS=-fstack-protector-all'

  CFLAGS: -fstack-protector-all -Wall
  LDFLAGS: -L$(top_srcdir)/lib   -L/usr/lib
  LIBS:  -lpcreposix -lpcre -lssl -lcrypto -lssl -lcrypto -lcap  -lGeoIP  -lssl  -lm -lpq  -lcrypto -lz -lsupp -lcrypt -ldl

  Files:
    Configuration File:
      /opt/cargo/etc/proftpd.conf
    Pid File:
      /var/run/proftpd.pid
    Scoreboard File:
      /opt/cargo/var/proftpd.scoreboard

  Features:
    - Autoshadow support
    + Controls support
    + curses support
    - Developer support
    - DSO support
    + IPv6 support
    + Largefile support
    - Lastlog support
    - Memcache support
    + ncurses support
    + NLS support
    + OpenSSL support
    + PCRE support
    + POSIX ACL support
    + Shadow file support
    + Sendfile support
    + Trace support

  Tunable Options:
    PR_TUNABLE_BUFFER_SIZE = 1024
    PR_TUNABLE_DEFAULT_RCVBUFSZ = 8192
    PR_TUNABLE_DEFAULT_SNDBUFSZ = 8192
    PR_TUNABLE_GLOBBING_MAX_MATCHES = 100000
    PR_TUNABLE_GLOBBING_MAX_RECURSION = 8
    PR_TUNABLE_HASH_TABLE_SIZE = 40
    PR_TUNABLE_NEW_POOL_SIZE = 512
    PR_TUNABLE_SCOREBOARD_BUFFER_SIZE = 80
    PR_TUNABLE_SCOREBOARD_SCRUB_TIMER = 30
    PR_TUNABLE_SELECT_TIMEOUT = 30
    PR_TUNABLE_TIMEOUTIDENT = 10
    PR_TUNABLE_TIMEOUTIDLE = 300
    PR_TUNABLE_TIMEOUTLINGER = 30
    PR_TUNABLE_TIMEOUTLOGIN = 300
    PR_TUNABLE_TIMEOUTNOXFER = 300
    PR_TUNABLE_TIMEOUTSTALLED = 1800
    PR_TUNABLE_XFER_SCOREBOARD_UPDATES = 10




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