krb5 commit: Handle all-zero tags in file2 rcache type

[Greg Hudson]

https://github.com/krb5/krb5/commit/6e1fdfb30bac750816da25d6dd4ed67d0149da12
commit 6e1fdfb30bac750816da25d6dd4ed67d0149da12
Author: Greg Hudson <ghudson at mit.edu>
Date:   Wed Jul 31 16:18:11 2019 -0400

    Handle all-zero tags in file2 rcache type
    
    In the unlikely case of an all-zero tag, rc_file2.c:store() could
    mistake an empty record for a replay.  Check that records from the
    file are non-empty (by checking that the timestamp is non-zero) before
    comparing them to the tag.
    
    ticket: 8786

 src/lib/krb5/rcache/rc_file2.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/lib/krb5/rcache/rc_file2.c b/src/lib/krb5/rcache/rc_file2.c
index 10f9a92..3240776 100644
--- a/src/lib/krb5/rcache/rc_file2.c
+++ b/src/lib/krb5/rcache/rc_file2.c
@@ -174,8 +174,8 @@ store(krb5_context context, int fd, const uint8_t tag[TAG_LEN], uint32_t now,
         if (ret)
             return ret;
 
-        if ((nread >= 1 && memcmp(r1tag, tag, TAG_LEN) == 0) ||
-            (nread == 2 && memcmp(r2tag, tag, TAG_LEN) == 0))
+        if ((nread >= 1 && r1stamp && memcmp(r1tag, tag, TAG_LEN) == 0) ||
+            (nread == 2 && r2stamp && memcmp(r2tag, tag, TAG_LEN) == 0))
             return KRB5KRB_AP_ERR_REPEAT;
 
         /* Make note of the first record available for writing (empty, beyond