FreeBSD Core dump: PAM authentication with Kerberos credentials (GSSAPI_MIT)
Aki Tuomi
aki.tuomi at dovecot.fi
Mon Feb 12 18:44:37 EET 2018
Hi!
Can you attempt to get core dump with debugging symbols with dovecot too? Currently it seems to only contain symbols from kerberos bit, which is not very useful on it's own.
Aki
> On 12 February 2018 at 17:34 Ben Woods <woodsb02 at gmail.com> wrote:
>
>
> Hi everyone,
>
> I have a repeatable core dump when running dovecot on FreeBSD in the
> specific scenario described below.
>
> Dovecot is linked against MIT kerberos in /usr/local/lib/, whilst PAM is
> linked against Heimdal in /usr/lib/.
> My expectation was that dovecot authentication using GSSAPI would use MIT
> kerberos in /usr/local/lib, whereas PAM authentication is independent from
> dovecot and would therefore use Herimdal in /usr/lib/.
>
> What actually seems to occur during PAM authentication is the Heimdal code
> in /usr/lib/ is initially being used, but part way through it switches to
> using the MIT kerberos code in /usr/local/lib/.
>
> I have reported this bug on the FreeBSD bug tracker here:
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=225818
>
> Any help troubleshooting this issue would be much appreciated. I suspect it
> has something to do with the CFLAGS and LDFLAGS being used during the
> build, so I have attached the build log to the FreeBSD bug report.
>
> Thanks in advance,
> Ben
>
>
> SCENARIO:
> - Build mail/dovecot with option GSSAPI_MIT (link against MIT kerberos from
> ports rather than Heimdal in base)
> - Configure dovecot for PAM authentication, using PAM service "imap":
> $ cat /usr/local/etc/dovecot/conf.d/10-auth.conf
> auth_mechanisms = plain
> passdb {
> driver = pam
> args = %s
> }
> userdb {
> driver = passwd
> }
> - Configure imap pam to authenticate against kerberos (and enable
> debugging):
> $ cat /etc/pam.d/imap
> auth sufficient pam_krb5.so debug
> account required pam_krb5.so debug
>
>
> RESULT:
> This results in a crash of the dovecot authentication worker before any
> kerberos messages are even exchanged.
>
>
> DIAGNOSIS:
> Reviewing the log output below, my explanation of the backtrace is below
> (cronological order / newest item last):
>
> - Dovecot had successfully performed pam_start(), the necessary
> pam_set_item(), and called pam_authenticate(pamh, 0)
> https://github.com/dovecot/core/blob/2.2.33.2/src/auth/passdb-pam.c#L158
>
> - PAM called pam_sm_authenticate() in
> /usr/lib/libpam/modules/pam_krb5/pam_krb5.c which successfully got the
> user, ruser, service, principal, password, checked local user, and then ran
> krb5_get_init_creds_opt_set_default_flags
> https://github.com/freebsd/freebsd/blob/master/lib/libpam/modules/pam_krb5/pam_krb5.c#L242
>
> - Heimdal krb5_get_init_creds_opt_set_default_flags ran the Heimdal version
> of krb5_appdefault_time:
> https://github.com/freebsd/freebsd/blob/master/crypto/heimdal/lib/krb5/init_creds.c#L171
>
> - Heimdal function krb5_appdefault_time ran the MIT kerberos version of
> krb5_appdefault_string:
> https://github.com/freebsd/freebsd/blob/master/crypto/heimdal/lib/krb5/appdefault.c#L130
>
> This is where the code path cross from using the Heimdal code to the MIT
> kerberos code, which it should not do. I know this, because the GDB
> backtrace shows the krb5_appdefault_string function called strdup in file
> appdefault.c:165, but the Heimdal appdefault.c file only has 140 lines.
> Reviewing the MIT kerberos code, the strdup function is indeed called at
> appdefault.c:165.
>
> Why did the Heimdal appdefault.c code call the MIT kerberos version of
> krb5_appdefault_string, when the Heimdal version was only 50 lines higher
> in the same appdefault.c file?
>
>
> ENVIRONMENT:
> $ dovecot -n
> # 2.2.33.2 (d6601f4ec): /usr/local/etc/dovecot/dovecot.conf
> # OS: FreeBSD 12.0-CURRENT amd64 zfs
> auth_debug = yes
> auth_debug_passwords = yes
> auth_krb5_keytab = /usr/local/etc/dovecot/dovecot.keytab
> auth_mechanisms = plain login gssapi
> auth_realms = WOODS.AM
> auth_verbose = yes
> mail_location = mdbox:/var/mail/%u
> namespace inbox {
> inbox = yes
> location =
> mailbox Drafts {
> special_use = \Drafts
> }
> mailbox Junk {
> special_use = \Junk
> }
> mailbox Sent {
> special_use = \Sent
> }
> mailbox "Sent Messages" {
> special_use = \Sent
> }
> mailbox Trash {
> special_use = \Trash
> }
> prefix =
> }
> passdb {
> args = failure_show_msg=yes %s
> driver = pam
> }
> service auth-worker {
> drop_priv_before_exec = yes
> }
> ssl_cert = </usr/local/etc/ssl/mail.woods.am/fullchain.pem
> ssl_key = # hidden, use -P to show it
> userdb {
> driver = passwd
> }
>
> GDB BACKTRACE OF COREDUMP:
> $ gdb /usr/local/libexec/dovecot/auth
> GNU gdb (GDB) 8.0.1 [GDB v8.0.1 for FreeBSD]
> Copyright (C) 2017 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html
> >
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law. Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "x86_64-portbld-freebsd12.0".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>.
> Find the GDB manual and other documentation resources online at:
> <http://www.gnu.org/software/gdb/documentation/>.
> For help, type "help".
> Type "apropos word" to search for commands related to "word"...
> Reading symbols from /usr/local/libexec/dovecot/auth...done.
> (gdb) core /tmp/auth.core
> [New LWP 102627]
> warning: Can't read pathname for load map: Unknown error: -1.
> warning: Can't read pathname for load map: Unknown error: -1.
> warning: Can't read pathname for load map: Unknown error: -1.
> warning: Can't read pathname for load map: Unknown error: -1.
> Core was generated by `dovecot/auth -w'.
> Program terminated with signal SIGSEGV, Segmentation fault.
> #0 strlen (str=0x0) at /usr/src/lib/libc/string/strlen.c:100
> warning: Source file is more recent than executable.
> 100 */
> (gdb) bt
> #0 strlen (str=0x0) at /usr/src/lib/libc/string/strlen.c:100
> #1 0x0000000012130022 in strdup (str=0x0) at
> /usr/src/lib/libc/string/strdup.c:46
> #2 0x0000000011b65e9d in krb5_appdefault_string (context=0x10777000,
> appname=0x106f0018 "imap", realm=0x0, option=0x13b1f403 "ticket_lifetime",
> default_value=0x0, ret_value=0x7fffffffe088)
> at appdefault.c:165
> #3 0x0000000013af4a80 in krb5_appdefault_time (context=0x0,
> appname=0xffffffffaaca6003 <error: Cannot access memory at address
> 0xffffffffaaca6003>,
> realm=0x50 <error: Cannot access memory at address 0x50>, option=0x0,
> def_val=0, ret_val=0x7fffffffe0e0) at
> /usr/src/crypto/heimdal/lib/krb5/appdefault.c:130
> #4 0x0000000013ae3e79 in krb5_get_init_creds_opt_set_default_flags
> (context=0x10777000, appname=0x106f0018 "imap", realm=0x0, opt=0x1070f3c0)
> at /usr/src/crypto/heimdal/lib/krb5/init_creds.c:171
> #5 0x00000000138b738f in ?? ()
> #6 0x0000000000000000 in ?? ()
>
>
> LOG OUTPUT:
> $ cat /var/log/maillog:
> Feb 11 09:20:40 mail dovecot: auth: Error: auth worker: Aborted PASSV
> request for woodsb02: Worker process died unexpectedly
> Feb 11 09:20:40 mail dovecot: auth-worker(34874): Fatal: master:
> service(auth-worker): child 34874 killed with signal 11 (core dumped)
> Feb 11 09:20:47 mail dovecot: imap-login: Disconnected (auth failed, 1
> attempts in 7 secs): user=<woodsb02>, method=PLAIN, rip=192.168.1.13,
> lip=192.168.1.13, TLS, session=<GRJsRuxkf17AqAEN>
>
> $ cat /var/log/debug.log:
> Feb 11 09:20:35 mail dovecot: auth: Debug: auth client connected
> (pid=34853)
> [34/1991]
> Feb 11 09:20:40 mail dovecot: auth: Debug: client in: AUTH 1
> PLAIN service=imap secured session=GRJsRuxkf17AqAEN
> lip=192.168.1.13 rip=192.168.1.13 lport=
> 993 rport=24191 resp=AHdvb2RzYjAyAHRlc3Q= (previous base64 data may
> contain sensitive data)
> Feb 11 09:20:40 mail dovecot: auth-worker(34874): Debug: Loading modules
> from directory: /usr/local/lib/dovecot/auth
> Feb 11 09:20:40 mail dovecot: auth-worker(34874): Debug: Module loaded:
> /usr/local/lib/dovecot/auth/lib20_auth_var_expand_crypt.so
> Feb 11 09:20:40 mail dovecot: auth-worker(34874): Debug:
> pam(woodsb02,192.168.1.13,<GRJsRuxkf17AqAEN>): lookup service=imap
> Feb 11 09:20:40 mail auth: in openpam_dispatch(): calling
> pam_sm_authenticate() in /usr/lib/pam_krb5.so.6
> Feb 11 09:20:40 mail auth: in pam_get_user(): entering
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_USER
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_get_user(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Got user:
> woodsb02
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_RUSER
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning
> PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Got ruser: woodsb02
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_SERVICE
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning
> PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Got service:
> imap
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Context
> initialised
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Done krb5_cc_register()
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'auth_as_self'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning
> NULL
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Created principal:
> woodsb02
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Done krb5_parse_name()
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Got principal:
> woodsb02 at WOODS.AM
> Feb 11 09:20:40 mail auth: in pam_get_authtok():
> entering
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering:
> PAM_RHOST
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning
> PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_HOST
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering:
> PAM_OLDAUTHTOK
>
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'try_first_pass'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'use_first_pass'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'authtok_prompt'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in openpam_subst(): entering: 'Password:'
> Feb 11 09:20:40 mail auth: in openpam_subst(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering: 'echo_pass'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in pam_vprompt(): entering
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_CONV
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_vprompt(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_set_item(): entering: PAM_AUTHTOK
> Feb 11 09:20:40 mail dovecot: auth-worker(34874): Debug:
> pam(woodsb02,192.168.1.13,<GRJsRuxkf17AqAEN>): #1/1 style=1 msg=Password:
> Feb 11 09:20:40 mail auth: in pam_set_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_get_item(): entering: PAM_AUTHTOK
> Feb 11 09:20:40 mail auth: in pam_get_item(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_get_authtok(): returning PAM_SUCCESS
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Got password
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'no_user_check'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in openpam_get_option(): entering:
> 'no_user_check'
> Feb 11 09:20:40 mail auth: in openpam_get_option(): returning NULL
> Feb 11 09:20:40 mail auth: in pam_sm_authenticate(): Done getpwnam()
> Feb 11 09:20:40 mail dovecot: auth-worker(34875): Debug: Loading modules
> from directory: /usr/local/lib/dovecot/auth
> Feb 11 09:20:40 mail dovecot: auth-worker(34875): Debug: Module loaded:
> /usr/local/lib/dovecot/auth/lib20_auth_var_expand_crypt.so
>
>
>
> $ ldd /usr/local/libexec/dovecot/auth
> /usr/local/libexec/dovecot/auth:
> libstats_auth.so => /usr/local/lib/dovecot/stats/libstats_auth.so
> (0x80089a000)
> libdovecot.so.0 => /usr/local/lib/dovecot/libdovecot.so.0
> (0x800a9c000)
> libcrypt.so.5 => /lib/libcrypt.so.5 (0x800e3a000)
> libpam.so.6 => /usr/lib/libpam.so.6 (0x801058000)
> libk5crypto.so.3.1 => /usr/local/lib/libk5crypto.so.3.1
> (0x801265000)
> libcom_err.so.3.0 => /usr/local/lib/libcom_err.so.3.0 (0x8014b3000)
> libldap-2.4.so.2 => /usr/local/lib/libldap-2.4.so.2 (0x8016b6000)
> liblber-2.4.so.2 => /usr/local/lib/liblber-2.4.so.2 (0x8018fc000)
> libkrb5.so.3.3 => /usr/local/lib/libkrb5.so.3.3 (0x801b0b000)
> libgssapi_krb5.so.2.2 => /usr/local/lib/libgssapi_krb5.so.2.2
> (0x801e27000)
> libc.so.7 => /lib/libc.so.7 (0x802090000)
> libkrb5support.so.0.1 => /usr/local/lib/libkrb5support.so.0.1
> (0x802679000)
> libintl.so.8 => /usr/local/lib/libintl.so.8 (0x802888000)
> libssl.so.44 => /usr/local/lib/libssl.so.44 (0x802a93000)
> libcrypto.so.42 => /usr/local/lib/libcrypto.so.42 (0x802ce7000)
>
> $ ldd /usr/lib/pam_krb5.so.6
> /usr/lib/pam_krb5.so.6:
> libkrb5.so.11 => /usr/lib/libkrb5.so.11 (0x801614000)
> libpam.so.6 => /usr/lib/libpam.so.6 (0x801892000)
> libc.so.7 => /lib/libc.so.7 (0x800826000)
> libasn1.so.11 => /usr/lib/libasn1.so.11 (0x801a9f000)
> libcom_err.so.5 => /usr/lib/libcom_err.so.5 (0x801d40000)
> libcrypt.so.5 => /lib/libcrypt.so.5 (0x801f42000)
> libcrypto.so.8 => /lib/libcrypto.so.8 (0x802200000)
> libhx509.so.11 => /usr/lib/libhx509.so.11 (0x80266e000)
> libroken.so.11 => /usr/lib/libroken.so.11 (0x8028bb000)
> libwind.so.11 => /usr/lib/libwind.so.11 (0x802ace000)
> libheimbase.so.11 => /usr/lib/libheimbase.so.11 (0x802cf6000)
> libprivateheimipcc.so.11 => /usr/lib/libprivateheimipcc.so.11
> (0x802efa000)
> libthr.so.3 => /lib/libthr.so.3 (0x8030fc000)
>
> --
> From: Benjamin Woods
> woodsb02 at gmail.com
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