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(ITS#8755) invalid file descriptor when closing tls connection

Full_Name: Christian Knueppel
Version: 2.4.45
OS: Ubuntu 16.04.3 LTS
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (

I currently developing on a c software which is using Openldap with TLS
authentication. My software is working fine, but when i test it with valgrind, i
always get an invalid file descriptor when closing the connection.

Here is the stacktrace from valgrind:
==17517== Warning: invalid file descriptor -1 in syscall write()
==17517==    at 0x4E4A4BD: ??? (syscall-template.S:84)
==17517==    by 0x61BF5E7: sb_debug_write (in
==17517==    by 0x7261644: _gnutls_writev_emu (gnutls_buffers.c:447)
==17517==    by 0x7261644: _gnutls_writev (gnutls_buffers.c:505)
==17517==    by 0x7261644: _gnutls_io_write_flush (gnutls_buffers.c:699)
==17517==    by 0x725BDFF: _gnutls_send_tlen_int (gnutls_record.c:464)
==17517==    by 0x727E0D7: _gnutls_send_int (gnutls_record.h:43)
==17517==    by 0x727E0D7: gnutls_alert_send (gnutls_alert.c:165)
==17517==    by 0x725DCD8: gnutls_bye (gnutls_record.c:289)
==17517==    by 0x5F9F181: tlsg_sb_close (in
==17517==    by 0x61C07B1: ber_int_sb_close (in
==17517==    by 0x61C08A3: ber_sockbuf_free (in
==17517==    by 0x5F815CD: ldap_ld_free (in
==17517==    by 0x41618F: ldap_close_handle (ldap_connection.c:481)

--> In function ldap_close_handle i call ldap_unbind_ext_s(ld, NULL, NULL).

The connection is built with ldap_initialize(&ld, config.ldap_url) and
ldap_start_tls_s(ld, NULL, NULL). Options set with ldap_set_option() are
LDAP_OPT_X_TLS_CACERTFILE are set to all SSL CA-Certificates
(/etc/ssl/certs/ca-certificates.crt). I run the ldap_unbind_ext_s command (for
test purpose) shortly after the start_tls command is finished.
When i use ldap_sasl_interactive_bind_s with DIGEST-MD5 instead of
ldap_start_tls_s, the warning doesn't appear. When i use both, tls and sasl, the
warning also appears.

My computer running on Ubuntu 16.04.3 LTS (uname: 4.4.0-97-generic x86_64) with
libldap-2.4-2 (2.4.42+dfsg-2ubuntu3.2) and libgnutls30 (3.4.10-4ubuntu1.4). I
also tested it with the newest Ubuntu Artful Aardvark and the newest openldap
(2.4.45+dfsg-1ubuntu1) and gnutls(3.5.8-6ubuntu3) release, but it didn't has any
effect in my case.

I also tryed to compiled openldap against openssl to see, if it might be a
gnutls bug, but the invalid file descriptor occurs again. The lower valgrind
stacktrace is done with openldap 2.4.45 and openssl 1.0.2g on the newest Artful
Aardvark 17.10.
==2638== Warning: invalid file descriptor -1 in syscall write()
==2638==    at 0x4E4DCC0: write (write.c:26)
==2638==    by 0x61C6E87: sb_debug_write (sockbuf.c:854)
==2638==    by 0x5FAAB4A: tlso_bio_write.part.8 (tls_o.c:790)
==2638==    by 0x516B94A: BIO_write (bio_lib.c:243)
==2638==    by 0x5B20C61: ssl3_write_pending (s3_pkt.c:1105)
==2638==    by 0x5B22E82: ssl3_dispatch_alert (s3_pkt.c:1733)
==2638==    by 0x5B1EAE6: ssl3_shutdown (s3_lib.c:4372)
==2638==    by 0x5FAA749: tlso_sb_close (tls_o.c:899)
==2638==    by 0x61C7D8A: ber_int_sb_close (sockbuf.c:383)
==2638==    by 0x61C7E73: ber_sockbuf_free (sockbuf.c:74)
==2638==    by 0x5F8D006: ldap_ld_free (unbind.c:134)
==2638==    by 0x1277B7: ldap_close_handle (ldap_connection.c:481)