krb5 commit [krb5-1.18]: Using locking in MEMORY krb5_cc_get_principal()

[Greg Hudson]

https://github.com/krb5/krb5/commit/4abb051f76ae8f55247875a68f424a62a6315ec0
commit 4abb051f76ae8f55247875a68f424a62a6315ec0
Author: Greg Hudson <ghudson at mit.edu>
Date:   Sun Jun 20 19:24:07 2021 -0400

    Using locking in MEMORY krb5_cc_get_principal()
    
    Without locking, the principal pointer could be freed out from under
    krb5_copy_principal() by another thread calling krb5_cc_initialize()
    or krb5_cc_destroy().
    
    (cherry picked from commit 1848447291c68e21311f441b0458ae53471d00d3)
    
    ticket: 9014
    version_fixed: 1.18.4

 src/lib/krb5/ccache/cc_memory.c |   17 +++++++++++------
 1 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/lib/krb5/ccache/cc_memory.c b/src/lib/krb5/ccache/cc_memory.c
index 9d13de9..6b07a2d 100644
--- a/src/lib/krb5/ccache/cc_memory.c
+++ b/src/lib/krb5/ccache/cc_memory.c
@@ -575,12 +575,17 @@ krb5_mcc_get_name (krb5_context context, krb5_ccache id)
 krb5_error_code KRB5_CALLCONV
 krb5_mcc_get_principal(krb5_context context, krb5_ccache id, krb5_principal *princ)
 {
-    krb5_mcc_data *ptr = (krb5_mcc_data *)id->data;
-    if (!ptr->prin) {
-        *princ = 0L;
-        return KRB5_FCC_NOFILE;
-    }
-    return krb5_copy_principal(context, ptr->prin, princ);
+    krb5_error_code ret;
+    krb5_mcc_data *d = id->data;
+
+    *princ = NULL;
+    k5_cc_mutex_lock(context, &d->lock);
+    if (d->prin == NULL)
+        ret = KRB5_FCC_NOFILE;
+    else
+        ret = krb5_copy_principal(context, d->prin, princ);
+    k5_cc_mutex_unlock(context, &d->lock);
+    return ret;
 }
 
 krb5_error_code KRB5_CALLCONV