Fail on non-signature lines in Release.gpg

The exploit for CVE-2019-3462 uses the fact that a Release.gpg file can
contain additional content beside the expected detached signature(s).
We were passing the file unchecked to gpgv which ignores these extras
without complains, so we reuse the same line-reading implementation we
use for InRelease splitting to detect if a Release.gpg file contains
unexpected data and fail in this case given that we in the previous
commit we established that we fail in the similar InRelease case now.

1 files changed, 43 insertions, 0 deletions

diff --git a/test/integration/test-cve-2019-3462-Release.gpg-payload b/test/integration/test-cve-2019-3462-Release.gpg-payload
new file mode 100755
index 000000000..fd0f96713
--- /dev/null
+++ b/test/integration/test-cve-2019-3462-Release.gpg-payload
@@ -0,0 +1,43 @@
+#!/bin/sh
+set -e
+
+# This is not covered by the CVE and harmless by itself, but used in
+# the exploit and while harmless it is also pointless to allow it
+
+TESTDIR="$(readlink -f "$(dirname "$0")")"
+. "$TESTDIR/framework"
+
+setupenvironment
+configarchitecture 'amd64'
+
+export APT_DONT_SIGN='InRelease'
+
+insertpackage 'unstable' 'foo' 'all' '1'
+setupaptarchive
+rm -rf rootdir/var/lib/apt/lists
+
+verify() {
+	testfailure apt update
+	testsuccess grep '^  Detached signature file' rootdir/tmp/testfailure.output
+	testfailure apt show foo
+}
+
+msgmsg 'Payload after detached signature'
+find aptarchive -name 'Release.gpg' | while read FILE; do
+	cp -a "$FILE" "${FILE}.bak"
+	echo "evil payload" >> "$FILE"
+done
+verify
+
+msgmsg 'Payload in-between detached signatures'
+find aptarchive -name 'Release.gpg' | while read FILE; do
+	cat "${FILE}.bak" >> "$FILE"
+done
+verify
+
+msgmsg 'Payload before detached signature'
+find aptarchive -name 'Release.gpg' | while read FILE; do
+	echo "evil payload" > "$FILE"
+	cat "${FILE}.bak" >> "$FILE"
+done
+verify