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, 5 insertions, 7 deletions

diff --git a/test/integration/test-apt-update-ims b/test/integration/test-apt-update-ims
index f091bffaa..7385e701a 100755
--- a/test/integration/test-apt-update-ims
+++ b/test/integration/test-apt-update-ims
@@ -43,7 +43,7 @@ runtest() {
     testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"
 
     # ensure that we still do a hash check for other files on ims hit of Release
-    if grep -q '^Hit .* \(InRelease\|Release.gpg\)$' expected.output ; then
+    if grep -q '^Hit .* InRelease$' expected.output || ! grep -q '^Ign .* Release\(\.gpg\)\?$' expected.output; then
 	    $TEST aptget update -o Debug::Acquire::gpgv=1
 	    cp rootdir/tmp/${TEST}.output goodsign.output
 	    testfileequal 'listsdir.lst' "$(listcurrentlistsdirectory)"
@@ -66,7 +66,6 @@ msgmsg 'Release/Release.gpg'
 EXPECT='Ign http://localhost:8080 unstable InRelease
   404  Not Found
 Hit http://localhost:8080 unstable Release
-Hit http://localhost:8080 unstable Release.gpg
 Reading package lists...'
 find aptarchive -name 'InRelease' -delete
 echo 'Acquire::GzipIndexes "0";' > rootdir/etc/apt/apt.conf.d/02compressindex
@@ -81,7 +80,7 @@ Hit http://localhost:8080 unstable Release
 Ign http://localhost:8080 unstable Release.gpg
   404  Not Found
 Reading package lists...
-W: The data from 'http://localhost:8080 unstable Release.gpg' is not signed. Packages from that repository can not be authenticated."
+W: The data from 'http://localhost:8080 unstable Release' is not signed. Packages from that repository can not be authenticated."
 find aptarchive -name 'Release.gpg' -delete
 echo 'Acquire::GzipIndexes "0";' > rootdir/etc/apt/apt.conf.d/02compressindex
 runtest 'warning'
@@ -108,8 +107,7 @@ msgmsg 'expired Release/Release.gpg'
 EXPECT='Ign http://localhost:8080 unstable InRelease
   404  Not Found
 Hit http://localhost:8080 unstable Release
-Hit http://localhost:8080 unstable Release.gpg
-E: Release file for http://localhost:8080/dists/unstable/Release.gpg is expired (invalid since). Updates for this repository will not be applied.'
+E: Release file for http://localhost:8080/dists/unstable/Release is expired (invalid since). Updates for this repository will not be applied.'
 find aptarchive -name 'InRelease' -delete
 echo 'Acquire::GzipIndexes "0";' > rootdir/etc/apt/apt.conf.d/02compressindex
 runtest 'failure'
@@ -122,8 +120,8 @@ EXPECT="Ign http://localhost:8080 unstable InRelease
 Hit http://localhost:8080 unstable Release
 Ign http://localhost:8080 unstable Release.gpg
   404  Not Found
-W: The data from 'http://localhost:8080 unstable Release.gpg' is not signed. Packages from that repository can not be authenticated.
-E: Release file for http://localhost:8080/dists/unstable/InRelease is expired (invalid since). Updates for this repository will not be applied."
+W: The data from 'http://localhost:8080 unstable Release' is not signed. Packages from that repository can not be authenticated.
+E: Release file for http://localhost:8080/dists/unstable/Release is expired (invalid since). Updates for this repository will not be applied."
 find aptarchive -name 'Release.gpg' -delete
 echo 'Acquire::GzipIndexes "0";' > rootdir/etc/apt/apt.conf.d/02compressindex
 runtest 'failure' 'warning'