handle gpgv's weak-digests ERRSIG

Our own gpgv method can declare a digest algorithm as untrusted and
handles these as worthless signatures. If gpgv comes with inbuilt
untrusted (which is called weak in official terminology) which it e.g.
does for MD5 in recent versions we should handle it in the same way.

To check this we use the most uncommon still fully trusted hash as a
configureable one via a hidden config option to toggle through all of
the three states a hash can be in.

methods/gpgv.cc

@@ -32,6 +32,7 @@ using std::vector;
 
 #define GNUPGPREFIX "[GNUPG:]"
 #define GNUPGBADSIG "[GNUPG:] BADSIG"
+#define GNUPGERRSIG "[GNUPG:] ERRSIG"
 #define GNUPGNOPUBKEY "[GNUPG:] NO_PUBKEY"
 #define GNUPGVALIDSIG "[GNUPG:] VALIDSIG"
 #define GNUPGGOODSIG "[GNUPG:] GOODSIG"
@@ -44,8 +45,20 @@ struct Digest {
       Untrusted,
       Weak,
       Trusted,
+      Configureable
    } state;
    char name[32];
+
+   State getState() const {
+      if (state != Digest::State::Configureable)
+	 return state;
+      std::string const digestconfig = _config->Find("Debug::Acquire::gpgv::configdigest::truststate", "trusted");
+      if (digestconfig == "weak")
+	 return State::Weak;
+      else if (digestconfig == "untrusted")
+	 return State::Untrusted;
+      return State::Trusted;
+   }
 };
 
 static constexpr Digest Digests[] = {
@@ -60,8 +73,9 @@ static constexpr Digest Digests[] = {
    {Digest::State::Trusted, "SHA256"},
    {Digest::State::Trusted, "SHA384"},
    {Digest::State::Trusted, "SHA512"},
-   {Digest::State::Trusted, "SHA224"},
+   {Digest::State::Configureable, "SHA224"},
 };
+static_assert(Digests[_count(Digests) - 1].state == Digest::State::Configureable, "the last digest algo isn't the configurable one which we expect for tests");
 
 static Digest FindDigest(std::string const & Digest)
 {
@@ -77,6 +91,10 @@ struct Signer {
    std::string key;
    std::string note;
 };
+static bool IsTheSameKey(std::string const &validsig, std::string const &goodsig) {
+   // VALIDSIG reports a keyid (40 = 24 + 16), GOODSIG is a longid (16) only
+   return validsig.compare(24, 16, goodsig, strlen("GOODSIG "), 16) == 0;
+}
 
 class GPGVMethod : public aptMethod
 {
@@ -91,7 +109,6 @@ class GPGVMethod : public aptMethod
    protected:
    virtual bool URIAcquire(std::string const &Message, FetchItem *Itm) APT_OVERRIDE;
    public:
-   
    GPGVMethod() : aptMethod("gpgv","1.0",SingleInstance | SendConfig) {};
 };
 
@@ -125,6 +142,7 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
 
    // Loop over the output of apt-key (which really is gnupg), and check the signatures.
    std::vector<std::string> ValidSigners;
+   std::vector<std::string> ErrSigners;
    size_t buffersize = 0;
    char *buffer = NULL;
    while (1)
@@ -144,11 +162,19 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
             std::clog << "Got BADSIG! " << std::endl;
          BadSigners.push_back(string(buffer+sizeof(GNUPGPREFIX)));
       }
+      else if (strncmp(buffer, GNUPGERRSIG, sizeof(GNUPGERRSIG)-1) == 0)
+      {
+         if (Debug == true)
+            std::clog << "Got ERRSIG " << std::endl;
+         ErrSigners.push_back(string(buffer, strlen(GNUPGPREFIX), strlen("ERRSIG ") + 16));
+      }
       else if (strncmp(buffer, GNUPGNOPUBKEY, sizeof(GNUPGNOPUBKEY)-1) == 0)
       {
          if (Debug == true)
             std::clog << "Got NO_PUBKEY " << std::endl;
          NoPubKeySigners.push_back(string(buffer+sizeof(GNUPGPREFIX)));
+	 ErrSigners.erase(std::remove_if(ErrSigners.begin(), ErrSigners.end(), [&](std::string const &errsig) {
+		  return errsig.compare(strlen("ERRSIG "), 16, buffer, strlen(GNUPGNOPUBKEY), 16) == 0;  }), ErrSigners.end());
       }
       else if (strncmp(buffer, GNUPGNODATA, sizeof(GNUPGBADSIG)-1) == 0)
       {
@@ -191,7 +217,7 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
          *p = 0;
          // Reject weak digest algorithms
          Digest digest = FindDigest(tokens[7]);
-         switch (digest.state) {
+         switch (digest.getState()) {
          case Digest::State::Weak:
             // Treat them like an expired key: For that a message about expiry
             // is emitted, a VALIDSIG, but no GOODSIG.
@@ -203,10 +229,12 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
             // Treat them like an expired key: For that a message about expiry
             // is emitted, a VALIDSIG, but no GOODSIG.
             WorthlessSigners.push_back(string(sig));
-            GoodSigners.erase(std::remove(GoodSigners.begin(), GoodSigners.end(), string(sig)));
+            GoodSigners.erase(std::remove_if(GoodSigners.begin(), GoodSigners.end(), [&](std::string const &goodsig) {
+		     return IsTheSameKey(string(sig), goodsig); }), GoodSigners.end());
 	    if (Debug == true)
 	       std::clog << "Got untrusted VALIDSIG, key ID: " << sig << std::endl;
             break;
+	 case Digest::State::Configureable:
          case Digest::State::Trusted:
 	    if (Debug == true)
 	       std::clog << "Got trusted VALIDSIG, key ID: " << sig << std::endl;
@@ -218,6 +246,7 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
    }
    fclose(pipein);
    free(buffer);
+   std::move(ErrSigners.begin(), ErrSigners.end(), std::back_inserter(WorthlessSigners));
 
    // apt-key has a --keyid parameter, but this requires gpg, so we call it without it
    // and instead check after the fact which keyids where used for verification
@@ -252,7 +281,22 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
    {
       ioprintf(std::clog, "gpgv exited with status %i\n", WEXITSTATUS(status));
    }
-   
+
+   if (Debug)
+   {
+      std::cerr << "Summary:" << std::endl << "  Good: ";
+      std::copy(GoodSigners.begin(), GoodSigners.end(), std::ostream_iterator<std::string>(std::cerr, ", "));
+      std::cerr << std::endl << "  Bad: ";
+      std::copy(BadSigners.begin(), BadSigners.end(), std::ostream_iterator<std::string>(std::cerr, ", "));
+      std::cerr << std::endl << "  Worthless: ";
+      std::copy(WorthlessSigners.begin(), WorthlessSigners.end(), std::ostream_iterator<std::string>(std::cerr, ", "));
+      std::cerr << std::endl << "  SoonWorthless: ";
+      std::for_each(SoonWorthlessSigners.begin(), SoonWorthlessSigners.end(), [](Signer const &sig) { std::cerr << sig.key << ", "; });
+      std::cerr << std::endl << "  NoPubKey: ";
+      std::copy(NoPubKeySigners.begin(), NoPubKeySigners.end(), std::ostream_iterator<std::string>(std::cerr, ", "));
+      std::cerr << std::endl;
+   }
+
    if (WEXITSTATUS(status) == 0)
    {
       if (keyIsID)
@@ -309,8 +353,7 @@ bool GPGVMethod::URIAcquire(std::string const &Message, FetchItem *Itm)
    // Check if all good signers are soon worthless and warn in that case
    if (std::all_of(GoodSigners.begin(), GoodSigners.end(), [&](std::string const &good) {
 	    return std::any_of(SoonWorthlessSigners.begin(), SoonWorthlessSigners.end(), [&](Signer const &weak) {
-		  // VALIDSIG reports a keyid (40 = 24 + 16), GOODSIG is a longid (16) only
-		  return weak.key.compare(24, 16, good, strlen("GOODSIG "), 16) == 0;
+		  return IsTheSameKey(weak.key, good);
 		  });
 	    }))
    {

test/integration/test-releasefile-verification

@@ -97,6 +97,7 @@ updatewithwarnings() {
 }
 
 runtest() {
+	local DELETEFILE="$1"
 	msgmsg 'Cold archive signed by' 'Joe Sixpack'
 	prepare "${PKGFILE}"
 	rm -rf rootdir/var/lib/apt/lists
@@ -257,19 +258,14 @@ runtest2() {
 }
 
 runtest3() {
-	export APT_TESTS_DIGEST_ALGO="$1"
-	msgmsg "Running base test with digest $1"
+	echo "Debug::Acquire::gpgv::configdigest::truststate \"$1\";" > rootdir/etc/apt/apt.conf.d/truststate
+	msgmsg "Running base test with $1 digest"
 	runtest2
 
-	DELETEFILE="InRelease"
-	msgmsg "Running test with deletion of $DELETEFILE and digest $1"
-	runtest
-
-	DELETEFILE="Release.gpg"
-	msgmsg "Running test with deletion of $DELETEFILE and digest $1"
-	runtest
-
-	unset APT_TESTS_DIGEST_ALGO
+	for DELETEFILE in 'InRelease' 'Release.gpg'; do
+		msgmsg "Running test with deletion of $DELETEFILE and $1 digest"
+		runtest "$DELETEFILE"
+	done
 }
 
 # diable some protection by default and ensure we still do the verification
@@ -278,17 +274,50 @@ cat > rootdir/etc/apt/apt.conf.d/weaken-security <<EOF
 Acquire::AllowInsecureRepositories "1";
 Acquire::AllowDowngradeToInsecureRepositories "1";
 EOF
+# the hash marked as configureable in our gpgv method
+export APT_TESTS_DIGEST_ALGO='SHA224'
 
-# an all-round good hash
 successfulaptgetupdate() {
 	testsuccess aptget update -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::gpgv=1
 }
-runtest3 'SHA512'
+runtest3 'trusted'
 
-# a hash we consider weak and therefore warn about
-rm -f rootdir/etc/apt/apt.conf.d/no-sha1
 successfulaptgetupdate() {
 	testwarning aptget update -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::gpgv=1
 	testsuccess grep 'uses weak digest algorithm' rootdir/tmp/testwarning.output
 }
-runtest3 'SHA1'
+runtest3 'weak'
+
+msgmsg "Running test with apt-untrusted digest"
+echo "Debug::Acquire::gpgv::configdigest::truststate \"untrusted\";" > rootdir/etc/apt/apt.conf.d/truststate
+runfailure() {
+	for DELETEFILE in 'InRelease' 'Release.gpg'; do
+		msgmsg 'Cold archive signed by' 'Joe Sixpack'
+		prepare "${PKGFILE}"
+		rm -rf rootdir/var/lib/apt/lists
+		signreleasefiles 'Joe Sixpack'
+		find aptarchive/ -name "$DELETEFILE" -delete
+		testfailure aptget update --no-allow-insecure-repositories -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::gpgv=1
+		testsuccess grep 'The following signatures were invalid' rootdir/tmp/testfailure.output
+		testnopackage 'apt'
+		testwarning aptget update --allow-insecure-repositories -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::gpgv=1
+		failaptold
+
+		msgmsg 'Cold archive signed by' 'Marvin Paranoid'
+		prepare "${PKGFILE}"
+		rm -rf rootdir/var/lib/apt/lists
+		signreleasefiles 'Marvin Paranoid'
+		find aptarchive/ -name "$DELETEFILE" -delete
+		testfailure aptget update --no-allow-insecure-repositories -o Debug::pkgAcquire::Worker=1 -o Debug::Acquire::gpgv=1
+		testnopackage 'apt'
+		updatewithwarnings '^W: .* NO_PUBKEY'
+		testsuccessequal "$(cat "${PKGFILE}")
+" aptcache show apt
+		failaptold
+	done
+}
+runfailure
+
+msgmsg "Running test with gpgv-untrusted digest"
+export APT_TESTS_DIGEST_ALGO='MD5'
+runfailure