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(ITS#6673) ldap_unbind() hangs on unreachable LDAP server when using TLS

Full_Name: Arthur de Jong
Version: 2.4.23
OS: Debian/unstable
Submission from: (NULL) (2001:888:1613:0:218:8bff:fe55:2c9f)

When a network connection to the LDAP server fails (is severed with iptables in
my set-up) the error is detected properly with ldap_result()
set), however closing the connection with ldap_unbind() hangs indefinitely on a
read() operation (determined by strace) when using a ldaps:// connection.

If the connection is opened without TLS ldap_unbind() only writes some data on
the connection and then closes it but with TLS it expects some response back.
Since read() is used this blocks.

This is a backtrace of the thread that was hanging:

#0  0xb7fe2424 in __kernel_vsyscall ()
#1  0xb7f5809b in read () at ../sysdeps/unix/syscall-template.S:82
#2  0xb7e021bb in sb_stream_read (sbiod=0x8064630, buf=0x8083038, len=5)
    at /build/buildd-openldap_2.4.23-6-i386-fyqRGs/openldap-2.4.23/libraries/liblber/sockbuf.c:493
#3  0xb7e0132a in sb_debug_read (sbiod=0x807e250, buf=0x8083038, len=5)
    at /build/buildd-openldap_2.4.23-6-i386-fyqRGs/openldap-2.4.23/libraries/liblber/sockbuf.c:827
#4  0xb7fa0d27 in tlsg_recv (ptr=0x806fb50, buf=0x8083038, len=4294966784) at
#5  0xb7c65aa2 in ?? () from /usr/lib/libgnutls.so.26
#6  0xb7c65f77 in ?? () from /usr/lib/libgnutls.so.26
#7  0xb7c611e7 in _gnutls_recv_int () from /usr/lib/libgnutls.so.26
#8  0xb7c626b8 in gnutls_bye () from /usr/lib/libgnutls.so.26
#9  0xb7fa0dc4 in tlsg_sb_close (sbiod=0x807e268) at tls_g.c:970
#10 0xb7e01831 in ber_int_sb_close (sb=0x80645a8)
    at /build/buildd-openldap_2.4.23-6-i386-fyqRGs/openldap-2.4.23/libraries/liblber/sockbuf.c:383
#11 0xb7f8d1a0 in ldap_free_connection (ld=0x8066418, lc=0x8065b60, force=1,
unbind=1) at request.c:768
#12 0xb7f83060 in ldap_ld_free (ld=0x8066418, close=1, sctrls=0x0, cctrls=0x0)
at unbind.c:93
#13 0xb7f83326 in ldap_unbind_ext (ld=0x8066418, sctrls=0x0, cctrls=0x0) at
#14 0xb7f8343f in ldap_unbind (ld=0x8066418) at unbind.c:69
#15 0x0804cfc0 in ?? ()
#16 0x0804e750 in ?? ()
#17 0x08057a9f in ?? ()
#18 0x0804bb8d in ?? ()
#19 0xb7f50955 in start_thread (arg=0xb7b92b70) at pthread_create.c:300
#20 0xb7ed0e7e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130

More background information is available at [0].

As a workaround [1] I've used LDAP_OPT_DESC to get the file descriptor for the
connection and used setsockopt(SO_RCVTIMEO) and setsockopt(SO_SNDTIMEO) on it.
This fixes the problem for me at least but I'm not 100% this has no unwanted

[0] http://bugs.debian.org/596983
[1] http://arthurdejong.org/viewvc/nss-pam-ldapd?view=rev&revision=1264