krb5 commit: Try compatible keys in rd_req_dec "any" path

[Greg Hudson]

https://github.com/krb5/krb5/commit/4f99c75eb6b1a53d78b26648e39309261e37755c
commit 4f99c75eb6b1a53d78b26648e39309261e37755c
Author: Nalin Dahyabhai <nalin at dahyabhai.net>
Date:   Tue Mar 18 16:39:47 2014 -0400

    Try compatible keys in rd_req_dec "any" path
    
    When we go to decrypt a ticket using a keytab, we have two code paths.
    
    In the first (traditional) one, we try to read an entry that exactly
    matches the principal name, enctype, and kvno from the ticket, and then
    attempt to decrypt the ticket using the entry's key.  The keytab
    routines helpfully return an entry so long as it's of a key type that's
    compatible with the ticket being decrypted, fixing up the enctype in the
    entry structure while doing so, allowing us to decrypt a DES-CBC-CRC
    ticket with a DES-CBC-MD5 key.
    
    In the second code path, we try the key of every entry which loosely
    matches the principal name from the ticket and which exactly matches its
    enctype, meaning that the ticket/keytab pair above won't work if the
    principal name is one which suggests we shouldn't be matching entries
    exactly.
    
    This change modifies the "any" path to also try to decrypt the ticket
    with compatible keys.
    
    [ghudson at mit.edu: avoid stuffing too much logic in one conditional]
    
    ticket: 7883 (new)

 src/lib/krb5/krb/rd_req_dec.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/src/lib/krb5/krb/rd_req_dec.c b/src/lib/krb5/krb/rd_req_dec.c
index 4b952f5..fbd088d 100644
--- a/src/lib/krb5/krb/rd_req_dec.c
+++ b/src/lib/krb5/krb/rd_req_dec.c
@@ -167,6 +167,8 @@ decrypt_ticket(krb5_context context, const krb5_ap_req *req,
     krb5_error_code ret;
     krb5_keytab_entry ent;
     krb5_kt_cursor cursor;
+    krb5_boolean similar;
+    krb5_enctype req_etype = req->ticket->enc_part.enctype;
 
 #ifdef LEAN_CLIENT
     return KRB5KRB_AP_WRONG_PRINC;
@@ -189,8 +191,12 @@ decrypt_ticket(krb5_context context, const krb5_ap_req *req,
         goto cleanup;
 
     while ((ret = krb5_kt_next_entry(context, keytab, &ent, &cursor)) == 0) {
-        if (ent.key.enctype == req->ticket->enc_part.enctype &&
+        ret = krb5_c_enctype_compare(context, ent.key.enctype, req_etype,
+                                     &similar);
+        if (ret == 0 && similar &&
             krb5_sname_match(context, server, ent.principal)) {
+            /* Coerce inexact matches to the request enctype. */
+            ent.key.enctype = req_etype;
             ret = try_one_entry(context, req, &ent, keyblock_out);
             if (ret == 0) {
                 TRACE_RD_REQ_DECRYPT_ANY(context, ent.principal, &ent.key);