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Try harder to avoid password change replay errors

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change_set_password() was changed to prefer TCP.  However, because
UDP_LAST falls back to UDP after one second, we can still get a replay
error due to a dropped packet, before the TCP layer has a chance to
retry.

Instead, try k5_sendto() with NO_UDP, and only fall back to UDP after
TCP fails completely without reaching a server.  In sendto_kdc.c,
implement an ONLY_UDP transport strategy to allow the UDP fallback.

Resolves: rhbz#2075186

Signed-off-by: Julien Rische <jrische@redhat.com>
This commit is contained in:
Julien Rische 2022-04-26 15:32:34 +02:00
parent 670d3af2d8
commit 4262e013b4
2 changed files with 97 additions and 1 deletions
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91
Try-harder-to-avoid-password-change-replay-errors.patch Normal file
View File

@ -0,0 +1,91 @@
From ad8e02485791023dcf66ef4612616f03895ceeb3 Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Fri, 4 Mar 2022 00:45:00 -0500
Subject: [PATCH] Try harder to avoid password change replay errors
Commit d7b3018d338fc9c989c3fa17505870f23c3759a8 (ticket 7905) changed
change_set_password() to prefer TCP. However, because UDP_LAST falls
back to UDP after one second, we can still get a replay error due to a
dropped packet, before the TCP layer has a chance to retry.
Instead, try k5_sendto() with NO_UDP, and only fall back to UDP after
TCP fails completely without reaching a server. In sendto_kdc.c,
implement an ONLY_UDP transport strategy to allow the UDP fallback.
ticket: 9037
---
src/lib/krb5/os/changepw.c | 9 ++++++++-
src/lib/krb5/os/os-proto.h | 1 +
src/lib/krb5/os/sendto_kdc.c | 12 ++++++++----
3 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/src/lib/krb5/os/changepw.c b/src/lib/krb5/os/changepw.c
index 9f968da7f..c59232586 100644
--- a/src/lib/krb5/os/changepw.c
+++ b/src/lib/krb5/os/changepw.c
@@ -255,9 +255,16 @@ change_set_password(krb5_context context,
callback_info.pfn_cleanup = kpasswd_sendto_msg_cleanup;
krb5_free_data_contents(callback_ctx.context, &chpw_rep);
+ /* UDP retransmits may be seen as replays. Only try UDP after other
+ * transports fail completely. */
code = k5_sendto(callback_ctx.context, NULL, &creds->server->realm,
- &sl, UDP_LAST, &callback_info, &chpw_rep,
+ &sl, NO_UDP, &callback_info, &chpw_rep,
ss2sa(&remote_addr), &addrlen, NULL, NULL, NULL);
+ if (code == KRB5_KDC_UNREACH) {
+ code = k5_sendto(callback_ctx.context, NULL, &creds->server->realm,
+ &sl, ONLY_UDP, &callback_info, &chpw_rep,
+ ss2sa(&remote_addr), &addrlen, NULL, NULL, NULL);
+ }
if (code)
goto cleanup;
diff --git a/src/lib/krb5/os/os-proto.h b/src/lib/krb5/os/os-proto.h
index a985f2aec..91d2791ce 100644
--- a/src/lib/krb5/os/os-proto.h
+++ b/src/lib/krb5/os/os-proto.h
@@ -49,6 +49,7 @@ typedef enum {
UDP_FIRST = 0,
UDP_LAST,
NO_UDP,
+ ONLY_UDP
} k5_transport_strategy;
/* A single server hostname or address. */
diff --git a/src/lib/krb5/os/sendto_kdc.c b/src/lib/krb5/os/sendto_kdc.c
index 0eedec175..c7f5d861a 100644
--- a/src/lib/krb5/os/sendto_kdc.c
+++ b/src/lib/krb5/os/sendto_kdc.c
@@ -802,11 +802,14 @@ resolve_server(krb5_context context, const krb5_data *realm,
int err, result;
char portbuf[PORT_LENGTH];
- /* Skip UDP entries if we don't want UDP. */
+ /* Skip entries excluded by the strategy. */
if (strategy == NO_UDP && entry->transport == UDP)
return 0;
+ if (strategy == ONLY_UDP && entry->transport != UDP &&
+ entry->transport != TCP_OR_UDP)
+ return 0;
- transport = (strategy == UDP_FIRST) ? UDP : TCP;
+ transport = (strategy == UDP_FIRST || strategy == ONLY_UDP) ? UDP : TCP;
if (entry->hostname == NULL) {
/* Added by a module, so transport is either TCP or UDP. */
ai.ai_socktype = socktype_for_transport(entry->transport);
@@ -850,8 +853,9 @@ resolve_server(krb5_context context, const krb5_data *realm,
}
/* For TCP_OR_UDP entries, add each address again with the non-preferred
- * transport, unless we are avoiding UDP. Flag these as deferred. */
- if (retval == 0 && entry->transport == TCP_OR_UDP && strategy != NO_UDP) {
+ * transport, if there is one. Flag these as deferred. */
+ if (retval == 0 && entry->transport == TCP_OR_UDP &&
+ (strategy == UDP_FIRST || strategy == UDP_LAST)) {
transport = (strategy == UDP_FIRST) ? TCP : UDP;
for (a = addrs; a != 0 && retval == 0; a = a->ai_next) {
a->ai_socktype = socktype_for_transport(transport);
--
2.35.1

7
krb5.spec
View File

@ -42,7 +42,7 @@
Summary: The Kerberos network authentication system
Name: krb5
Version: 1.19.1
Release: %{?zdpd}17%{?dist}
Release: %{?zdpd}18%{?dist}
# rharwood has trust path to signing key and verifies on check-in
Source0: https://web.mit.edu/kerberos/dist/krb5/%{version}/krb5-%{version}%{?dashpre}.tar.gz
@ -92,6 +92,7 @@ Patch27: Fix-KDC-null-deref-on-bad-encrypted-challenge.patch
Patch28: Fix-KDC-null-deref-on-TGS-inner-body-null-server.patch
Patch29: Use-SHA256-instead-of-SHA1-for-PKINIT-CMS-digest.patch
Patch30: downstream-Use-newly-enforced-dejagnu-path-naming-convention.patch
Patch31: Try-harder-to-avoid-password-change-replay-errors.patch
License: MIT
URL: https://web.mit.edu/kerberos/www/
@ -648,6 +649,10 @@ exit 0
%{_libdir}/libkadm5srv_mit.so.*
%changelog
* Tue Apr 26 2022 Julien Rische <jrische@redhat.com> - 1.19.1-18
- Try harder to avoid password change replay errors
- Resolves: rhbz#2075186
* Mon Mar 14 2022 Julien Rische <jrische@redhat.com> - 1.19.1-15
- Use SHA-256 instead of SHA-1 for PKINIT CMS digest