From 722b77ba31ea4e2937e6820f0fe4a19a7445e8fc Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Tue, 15 Dec 2020 12:56:18 -0500
Subject: [PATCH] Preserve cred order in memory ccache type

In the memory credential cache type, add new creds to the tail of the
list so that iteration does not reverse the order.
---
 src/lib/krb5/ccache/cc_memory.c | 11 +++++++--
 src/lib/krb5/ccache/t_cc.c      | 43 +++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/src/lib/krb5/ccache/cc_memory.c b/src/lib/krb5/ccache/cc_memory.c
index 610091a257..529ada5455 100644
--- a/src/lib/krb5/ccache/cc_memory.c
+++ b/src/lib/krb5/ccache/cc_memory.c
@@ -108,6 +108,7 @@ typedef struct _krb5_mcc_data {
     k5_cc_mutex lock;
     krb5_principal prin;
     krb5_mcc_link *link;
+    krb5_mcc_link **tail;       /* Where to store next added cred */
     /* Time offsets for clock-skewed clients.  */
     krb5_int32 time_offset;
     krb5_int32 usec_offset;
@@ -159,6 +160,7 @@ empty_mcc_cache(krb5_context context, krb5_mcc_data *d)
         free(curr);
     }
     d->link = NULL;
+    d->tail = &d->link;
     d->generation++;
     krb5_free_principal(context, d->prin);
     d->prin = NULL;
@@ -470,6 +472,7 @@ new_mcc_data (const char *name, krb5_mcc_data **dataptr)
         return KRB5_CC_NOMEM;
     }
     d->link = NULL;
+    d->tail = &d->link;
     d->prin = NULL;
     d->time_offset = 0;
     d->usec_offset = 0;
@@ -665,13 +668,17 @@ krb5_mcc_store(krb5_context ctx, krb5_ccache id, krb5_creds *creds)
     new_node = malloc(sizeof(krb5_mcc_link));
     if (new_node == NULL)
         return ENOMEM;
+    new_node->next = NULL;
     err = krb5_copy_creds(ctx, creds, &new_node->creds);
     if (err)
         goto cleanup;
+
+    /* Place the new node at the tail of the list. */
     k5_cc_mutex_lock(ctx, &mptr->lock);
-    new_node->next = mptr->link;
-    mptr->link = new_node;
+    *mptr->tail = new_node;
+    mptr->tail = &new_node->next;
     k5_cc_mutex_unlock(ctx, &mptr->lock);
+
     return 0;
 cleanup:
     free(new_node);
diff --git a/src/lib/krb5/ccache/t_cc.c b/src/lib/krb5/ccache/t_cc.c
index a7251e273e..267725240d 100644
--- a/src/lib/krb5/ccache/t_cc.c
+++ b/src/lib/krb5/ccache/t_cc.c
@@ -560,6 +560,47 @@ test_memory_concurrent(krb5_context context)
     free_test_cred(context);
 }
 
+/* Check that order is preserved during iteration.  Not all cache types have
+ * this property. */
+static void
+test_order(krb5_context context, const char *name)
+{
+    krb5_error_code kret;
+    krb5_ccache id;
+    krb5_cc_cursor cursor;
+    krb5_creds creds;
+
+    kret = init_test_cred(context);
+    CHECK(kret, "init_creds");
+
+    kret = krb5_cc_resolve(context, name, &id);
+    CHECK(kret, "resolve");
+    kret = krb5_cc_initialize(context, id, test_creds.client);
+    CHECK(kret, "initialize");
+    kret = krb5_cc_store_cred(context, id, &test_creds);
+    CHECK(kret, "store 1");
+    kret = krb5_cc_store_cred(context, id, &test_creds2);
+    CHECK(kret, "store 2");
+
+    kret = krb5_cc_start_seq_get(context, id, &cursor);
+    CHECK(kret, "start_seq_get");
+    kret = krb5_cc_next_cred(context, id, &cursor, &creds);
+    CHECK(kret, "next_cred 1");
+    CHECK_BOOL(krb5_principal_compare(context, creds.server,
+                                      test_creds.server) != TRUE,
+               "first cred does not match", "principal_compare");
+    krb5_free_cred_contents(context, &creds);
+
+    kret = krb5_cc_next_cred(context, id, &cursor, &creds);
+    CHECK(kret, "next_cred 2");
+    CHECK_BOOL(krb5_principal_compare(context, creds.server,
+                                      test_creds2.server) != TRUE,
+               "second cred does not match", "principal_compare");
+    krb5_free_cred_contents(context, &creds);
+
+    free_test_cred(context);
+}
+
 extern const krb5_cc_ops krb5_mcc_ops;
 extern const krb5_cc_ops krb5_fcc_ops;
 
@@ -610,6 +651,8 @@ main(void)
 
     test_memory_concurrent(context);
 
+    test_order(context, "MEMORY:order");
+
     krb5_free_context(context);
     return 0;
 }
-- 
2.47.2