From 4566aaf97f5b4143b930d75628f3abc905249dcd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Wed, 5 Dec 2018 22:45:02 +0100
Subject: [PATCH] journald: set a limit on the number of fields (1k)

We allocate a iovec entry for each field, so with many short entries,
our memory usage and processing time can be large, even with a relatively
small message size. Let's refuse overly long entries.

CVE-2018-16865
https://bugzilla.redhat.com/show_bug.cgi?id=1653861

What from I can see, the problem is not from an alloca, despite what the CVE
description says, but from the attack multiplication that comes from creating
many very small iovecs: (void* + size_t) for each three bytes of input message.

Patch backported from systemd master at
052c57f132f04a3cf4148f87561618da1a6908b4.
---
 src/basic/journal-importer.h  | 3 +++
 src/journal/journald-native.c | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/src/basic/journal-importer.h b/src/basic/journal-importer.h
index f49ce734a1..c4ae45d32d 100644
--- a/src/basic/journal-importer.h
+++ b/src/basic/journal-importer.h
@@ -16,6 +16,9 @@
 #define DATA_SIZE_MAX (1024*1024*768u)
 #define LINE_CHUNK 8*1024u
 
+/* The maximum number of fields in an entry */
+#define ENTRY_FIELD_COUNT_MAX 1024
+
 struct iovec_wrapper {
         struct iovec *iovec;
         size_t size_bytes;
diff --git a/src/journal/journald-native.c b/src/journal/journald-native.c
index 5ff22a10af..951d092053 100644
--- a/src/journal/journald-native.c
+++ b/src/journal/journald-native.c
@@ -140,6 +140,11 @@ static int server_process_entry(
                 }
 
                 /* A property follows */
+                if (n > ENTRY_FIELD_COUNT_MAX) {
+                        log_debug("Received an entry that has more than " STRINGIFY(ENTRY_FIELD_COUNT_MAX) " fields, ignoring entry.");
+                        r = 1;
+                        goto finish;
+                }
 
                 /* n existing properties, 1 new, +1 for _TRANSPORT */
                 if (!GREEDY_REALLOC(iovec, m,
-- 
2.11.0