[Impala-ASF-CR] IMPALA-8212 / KUDU-2706: Work around the lack of thread safety in krb5 parse name()

["Michael Ho (Code Review)" <ge...@cloudera.org>]

Hello Thomas Marshall, Alexey Serbin, Kudu Jenkins, Impala Public Jenkins, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/12553

to look at the new patch set (#2).

Change subject: IMPALA-8212 / KUDU-2706: Work around the lack of thread safety in krb5_parse_name()
......................................................................

IMPALA-8212 / KUDU-2706: Work around the lack of thread safety in krb5_parse_name()

krb5_init_context() sets the field 'default_realm' in a krb5_context
object to 0. Upon first call to krb5_parse_name() with a principal
without realm specified (e.g. foo/bar), 'default_realm' in the
krb5_context object is lazily initialized.

When more than one negotiation threads are configured, it's possible
for multiple threads to call CanonicalizeKrb5Principal() in parallel.
CanonicalizeKrb5Principal() in turn calls krb5_parse_name(g_krb5_ctx, ...)
with no lock held. In addition, krb5_parse_name() is not thread safe as
it lazily initializes 'context->default_realm' without holding lock.
Consequently, 'g_krb5_ctx' which is shared and not supposed to be modified
after initialization may be inadvertently modified concurrently by multiple
threads, leading to crashes (e.g. double free) or errors.

This change works around the problem by initializing 'g_krb5_ctx->default_realm'
once in InitKrb5Ctx() by calling krb5_get_default_realm().

Impala internally calls InitAuth() which calls InitKerberosForServer()
which ends up calling InitKrb5Ctx() in a single threaded environment.

Change-Id: I1bf9224516e2996f51f319088179727f76741ebe
Reviewed-on: http://gerrit.cloudera.org:8080/12545
Reviewed-by: Alexey Serbin <as...@cloudera.com>
Tested-by: Kudu Jenkins
---
M be/src/kudu/security/init.cc
1 file changed, 12 insertions(+), 0 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/53/12553/2
-- 
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I1bf9224516e2996f51f319088179727f76741ebe
Gerrit-Change-Number: 12553
Gerrit-PatchSet: 2
Gerrit-Owner: Michael Ho <kw...@cloudera.com>
Gerrit-Reviewer: Alexey Serbin <as...@cloudera.com>
Gerrit-Reviewer: Impala Public Jenkins <im...@cloudera.com>
Gerrit-Reviewer: Kudu Jenkins (120)
Gerrit-Reviewer: Thomas Marshall <tm...@cloudera.com>