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Message #69290
[Bug 1103353] Re: Invalid GnuTLS cipher suite strings causes libldap to crash
Marking Won't Fix for SRUs as per Oleg's request. I don't see any real
user impact to this bug here that would justify an SRU. Harry's case
might be valid, but as Oleg was unable to reproduce and we don't have
reproduction steps we wouldn't be able to pass SRU verification anyway.
If somebody would like to post detailed steps to reproduce this bug that
also demonstrates a use case which does create a real user impact, then
I'd be happy to reconsider.
** Changed in: openldap (Ubuntu Precise)
Status: In Progress => Won't Fix
** Changed in: openldap (Ubuntu Trusty)
Status: In Progress => Won't Fix
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https://bugs.launchpad.net/bugs/1103353
Title:
Invalid GnuTLS cipher suite strings causes libldap to crash
Status in openldap package in Ubuntu:
Fix Released
Status in openldap source package in Precise:
Won't Fix
Status in openldap source package in Trusty:
Won't Fix
Status in openldap package in Debian:
Fix Released
Bug description:
If the cipher suite string is unacceptable to GnuTLS, libldap_r-2.4
crashes due to a double free. GnuTLS is extremely picky about the
cipher suite strings it accepts; as a first measure, try LDAP cipher
suite string "SECURE256" or "NORMAL". If that stops the crash, then
you have encountered this bug.
Typically, the crash report begins with something like
*** glibc detected *** APPLICATION: double free or corruption (!prev)
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7fc68cff0b96]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(+0x38769)[0x7fc68bb13769]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(+0x3570e)[0x7fc68bb1070e]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(ldap_pvt_tls_init_def_ctx+0x1d)[0x7fc68bb108ed]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(+0x35965)[0x7fc68bb10965]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(+0x35a6d)[0x7fc68bb10a6d]
/usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2(ldap_int_tls_start+0x5d)[0x7fc68bb1149d]
The actual double free happens in
openldap/libraries/libldap/tls2.c:ldap_int_tls_init_ctx(), in the
ldap_pvt_tls_ctx_free(lo->ldo_tls_ctx); call in the error_exit: path.
The root cause of the double free is lack of GnuTLS return value
checks when calling gnutls_priority*() functions. The code simply
assumes they succeed, and when GnuTLS fails to provide a valid context
due to those failures, ldap_int_tls_init_ctx() tries to free the
never-fully-initialized context.
A simple fix is to create GnuTLS security contexts using the
configured cipher suite string, instead of "NORMAL" as
openldap/libraries/libldap/tls_g.c now does. If the cipher suite
string is invalid, then do not create the context at all. This is
caught earlier in ldap_int_tls_init_ctx(), and avoids the crash.
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