treat older Release files than we already have as an IMSHit

Valid-Until protects us from long-living downgrade attacks, but not all
repositories have it and an attacker could still use older but still
valid files to downgrade us. While this makes it sounds like a security
improvement now, its a bit theoretical at best as an attacker with
capabilities to pull this off could just as well always keep us days
(but in the valid period) behind and always knows which state we have,
as we tell him with the If-Modified-Since header. This is also why this
is 'silently' ignored and treated as an IMSHit rather than screamed at
the user as this can at best be an annoyance for attackers.

An error here would 'regularily' be encountered by users by out-of-sync
mirrors serving a single run (e.g. load balancer) or in two consecutive
runs on the other hand, so it would just help teaching people ignore it.

That said, most of the code churn is caused by enforcing this additional
requirement. Crisscross from InRelease to Release.gpg is e.g. very
unlikely in practice, but if we would ignore it an attacker could
sidestep it this way.

1 files changed, 62 insertions, 0 deletions

diff --git a/test/integration/test-releasefile-date-older b/test/integration/test-releasefile-date-older
new file mode 100755
index 000000000..5cdc34fac
--- /dev/null
+++ b/test/integration/test-releasefile-date-older
@@ -0,0 +1,62 @@
+#!/bin/sh
+set -e
+
+TESTDIR=$(readlink -f $(dirname $0))
+. $TESTDIR/framework
+setupenvironment
+configarchitecture 'i386'
+
+insertpackage 'wheezy' 'apt' 'all' '0.8.15'
+
+setupaptarchive --no-update
+
+# we don't complain as the server could have just sent a 'Hit' here and this
+# 'downgrade attack' is usually performed by out-of-sync mirrors. Valid-Until
+# catches the 'real' downgrade attacks (expect that it finds stale mirrors).
+# Scaring users with an error here serves hence no point.
+
+msgmsg 'InRelease file is silently rejected if' 'new Date is before old Date'
+rm -rf rootdir/var/lib/apt/lists
+generatereleasefiles 'now' 'now + 7 days'
+signreleasefiles
+testsuccess aptget update
+listcurrentlistsdirectory > listsdir.lst
+redatereleasefiles 'now - 2 days'
+testsuccess aptget update
+testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"
+
+msgmsg 'Release.gpg file is silently rejected if' 'new Date is before old Date'
+rm -rf rootdir/var/lib/apt/lists
+generatereleasefiles 'now' 'now + 7 days'
+signreleasefiles
+find aptarchive -name 'InRelease' -delete
+testsuccess aptget update
+listcurrentlistsdirectory > listsdir.lst
+redatereleasefiles 'now - 2 days'
+find aptarchive -name 'InRelease' -delete
+testsuccess aptget update
+testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"
+
+msgmsg 'Crisscross InRelease/Release.gpg file is silently rejected if' 'new Date is before old Date'
+rm -rf rootdir/var/lib/apt/lists
+generatereleasefiles 'now' 'now + 7 days'
+signreleasefiles
+find aptarchive -name 'Release.gpg' -delete
+testsuccess aptget update
+listcurrentlistsdirectory > listsdir.lst
+redatereleasefiles 'now - 2 days'
+find aptarchive -name 'InRelease' -delete
+testsuccess aptget update
+testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"
+
+msgmsg 'Crisscross Release.gpg/InRelease file is silently rejected if' 'new Date is before old Date'
+rm -rf rootdir/var/lib/apt/lists
+generatereleasefiles 'now' 'now + 7 days'
+signreleasefiles
+find aptarchive -name 'InRelease' -delete
+testsuccess aptget update
+listcurrentlistsdirectory > listsdir.lst
+redatereleasefiles 'now - 2 days'
+find aptarchive -name 'Release.gpg' -delete
+testsuccess aptget update
+testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"