implement Signed-By option for sources.list

Limits which key(s) can be used to sign a repository. Not immensely useful
from a security perspective all by itself, but if the user has
additional measures in place to confine a repository (like pinning) an
attacker who gets the key for such a repository is limited to its
potential and can't use the key to sign its attacks for an other (maybe
less limited) repository… (yes, this is as weak as it sounds, but having
the capability might come in handy for implementing other stuff later).

apt-pkg/acquire-item.cc

@@ -808,7 +808,6 @@ string pkgAcqMetaBase::Custom600Headers() const
    Header += MaximumSize;
 
    string const FinalFile = GetFinalFilename();
-
    struct stat Buf;
    if (stat(FinalFile.c_str(),&Buf) == 0)
       Header += "\nLast-Modified: " + TimeRFC1123(Buf.st_mtime);
@@ -1132,6 +1131,10 @@ string pkgAcqMetaClearSig::Custom600Headers() const
 {
    string Header = pkgAcqMetaBase::Custom600Headers();
    Header += "\nFail-Ignore: true";
+   std::string const key = TransactionManager->MetaIndexParser->GetSignedBy();
+   if (key.empty() == false)
+      Header += "\nSigned-By: " + key;
+
    return Header;
 }
 									/*}}}*/
@@ -1372,6 +1375,16 @@ pkgAcqMetaSig::pkgAcqMetaSig(pkgAcquire * const Owner,
 									/*}}}*/
 pkgAcqMetaSig::~pkgAcqMetaSig()						/*{{{*/
 {
+}
+									/*}}}*/
+// pkgAcqMetaSig::Custom600Headers - Insert custom request headers	/*{{{*/
+std::string pkgAcqMetaSig::Custom600Headers() const
+{
+   std::string Header = pkgAcqTransactionItem::Custom600Headers();
+   std::string const key = TransactionManager->MetaIndexParser->GetSignedBy();
+   if (key.empty() == false)
+      Header += "\nSigned-By: " + key;
+   return Header;
 }
 									/*}}}*/
 // AcqMetaSig::Done - The signature was downloaded/verified		/*{{{*/

apt-pkg/acquire-item.h

@@ -541,6 +541,7 @@ class APT_HIDDEN pkgAcqMetaSig : public pkgAcqTransactionItem
    virtual void Failed(std::string const &Message,pkgAcquire::MethodConfig const * const Cnf);
    virtual void Done(std::string const &Message, HashStringList const &Hashes,
 		     pkgAcquire::MethodConfig const * const Cnf);
+   virtual std::string Custom600Headers() const;
 
    /** \brief Create a new pkgAcqMetaSig. */
    pkgAcqMetaSig(pkgAcquire * const Owner, pkgAcqMetaClearSig * const TransactionManager,

apt-pkg/contrib/gpgv.cc

@@ -16,6 +16,8 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <stddef.h>
+
+#include <algorithm>
 #include <iostream>
 #include <string>
 #include <vector>
@@ -42,7 +44,7 @@ static char * GenerateTemporaryFileTemplate(const char *basename)	/*{{{*/
    of the lifting in regards to merging keyrings. Fun for the whole family.
 */
 void ExecGPGV(std::string const &File, std::string const &FileGPG,
-             int const &statusfd, int fd[2])
+             int const &statusfd, int fd[2], std::string const &key)
 {
    #define EINTERNAL 111
    std::string const aptkey = _config->FindFile("Dir::Bin::apt-key", "/usr/bin/apt-key");
@@ -55,6 +57,19 @@ void ExecGPGV(std::string const &File, std::string const &FileGPG,
    Args.push_back(aptkey.c_str());
    Args.push_back("--quiet");
    Args.push_back("--readonly");
+   if (key.empty() == false)
+   {
+      if (key[0] == '/')
+      {
+	 Args.push_back("--keyring");
+	 Args.push_back(key.c_str());
+      }
+      else
+      {
+	 Args.push_back("--keyid");
+	 Args.push_back(key.c_str());
+      }
+   }
    Args.push_back("verify");
 
    char statusfdstr[10];

apt-pkg/contrib/gpgv.h

@@ -38,9 +38,12 @@ class FileFd;
  *
  * @param File is the message (unsigned or clear-signed)
  * @param FileSig is the signature (detached or clear-signed)
+ * @param statusfd is the fd given to gpgv as --status-fd
+ * @param fd is used as a pipe for the standard output of gpgv
+ * @param key is the specific one to be used instead of using all
  */
 void ExecGPGV(std::string const &File, std::string const &FileSig,
-      int const &statusfd, int fd[2]) APT_NORETURN;
+      int const &statusfd, int fd[2], std::string const &Key = "") APT_NORETURN;
 inline APT_NORETURN void ExecGPGV(std::string const &File, std::string const &FileSig,
       int const &statusfd = -1) {
    int fd[2];

apt-pkg/deb/debmetaindex.cc

@@ -461,6 +461,29 @@ bool debReleaseIndex::SetValidUntilMax(time_t const Valid)
    else if (d->ValidUntilMax != Valid)
       return _error->Error(_("Conflicting values set for option %s concerning source %s %s"), "Max-ValidTime", URI.c_str(), Dist.c_str());
    return true;
+}
+bool debReleaseIndex::SetSignedBy(std::string const &pSignedBy)
+{
+   if (SignedBy.empty() == true && pSignedBy.empty() == false)
+   {
+      if (pSignedBy[0] == '/') // no check for existence as we could be chrooting later or such things
+	 ; // absolute path to a keyring file
+      else
+      {
+	 // we could go all fancy and allow short/long/string matches as gpgv/apt-key does,
+	 // but fingerprints are harder to fake than the others and this option is set once,
+	 // not interactively all the time so easy to type is not really a concern.
+	 std::string finger = pSignedBy;
+	 finger.erase(std::remove(finger.begin(), finger.end(), ' '), finger.end());
+	 std::transform(finger.begin(), finger.end(), finger.begin(), ::toupper);
+	 if (finger.length() != 40 || finger.find_first_not_of("0123456789ABCDEF") != std::string::npos)
+	    return _error->Error(_("Invalid value set for option %s concerning source %s %s (%s)"), "Signed-By", URI.c_str(), Dist.c_str(), "not a fingerprint");
+      }
+      SignedBy = pSignedBy;
+   }
+   else if (SignedBy != pSignedBy)
+      return _error->Error(_("Conflicting values set for option %s concerning source %s %s"), "Signed-By", URI.c_str(), Dist.c_str());
+   return true;
 }
 									/*}}}*/
 // ReleaseIndex::IsTrusted						/*{{{*/
@@ -706,6 +729,18 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 	 Deb->SetValidUntilMin(GetTimeOption(Options, "valid-until-min")) == false)
 	 return false;
 
+      std::map<std::string, std::string>::const_iterator const signedby = Options.find("signed-by");
+      if (signedby == Options.end())
+      {
+	 if (Deb->SetSignedBy("") == false)
+	    return false;
+      }
+      else
+      {
+	 if (Deb->SetSignedBy(signedby->second) == false)
+	    return false;
+      }
+
       return true;
    }
 

apt-pkg/deb/debmetaindex.h

@@ -56,6 +56,7 @@ class APT_HIDDEN debReleaseIndex : public metaIndex
    bool SetCheckValidUntil(TriState const Trusted);
    bool SetValidUntilMin(time_t const Valid);
    bool SetValidUntilMax(time_t const Valid);
+   bool SetSignedBy(std::string const &SignedBy);
 
    virtual bool IsTrusted() const;
 

apt-pkg/metaindex.cc

@@ -27,8 +27,7 @@ bool metaIndex::Merge(pkgCacheGenerator &Gen,OpProgress *) const
 metaIndex::metaIndex(std::string const &URI, std::string const &Dist,
       char const * const Type)
 : d(NULL), Indexes(NULL), Type(Type), URI(URI), Dist(Dist), Trusted(TRI_UNSET),
-   LoadedSuccessfully(TRI_UNSET),
-   Date(0), ValidUntil(0), SupportsAcquireByHash(false)
+   Date(0), ValidUntil(0), SupportsAcquireByHash(false), LoadedSuccessfully(TRI_UNSET)
 {
    /* nothing */
 }
@@ -48,6 +47,7 @@ APT_PURE std::string metaIndex::GetURI() const { return URI; }
 APT_PURE std::string metaIndex::GetDist() const { return Dist; }
 APT_PURE const char* metaIndex::GetType() const { return Type; }
 APT_PURE metaIndex::TriState metaIndex::GetTrusted() const { return Trusted; }
+APT_PURE std::string metaIndex::GetSignedBy() const { return SignedBy; }
 APT_PURE std::string metaIndex::GetCodename() const { return Codename; }
 APT_PURE std::string metaIndex::GetSuite() const { return Suite; }
 APT_PURE bool metaIndex::GetSupportsAcquireByHash() const { return SupportsAcquireByHash; }

apt-pkg/metaindex.h

@@ -52,7 +52,7 @@ class metaIndex
    std::string URI;
    std::string Dist;
    TriState Trusted;
-   TriState LoadedSuccessfully;
+   std::string SignedBy;
 
    // parsed from a file
    std::string Suite;
@@ -61,13 +61,15 @@ class metaIndex
    time_t ValidUntil;
    bool SupportsAcquireByHash;
    std::map<std::string, checkSum *> Entries;
+   TriState LoadedSuccessfully;
 
 public:
    // Various accessors
    std::string GetURI() const;
    std::string GetDist() const;
    const char* GetType() const;
    TriState GetTrusted() const;
+   std::string GetSignedBy() const;
 
    std::string GetCodename() const;
    std::string GetSuite() const;

apt-pkg/sourcelist.cc

@@ -93,27 +93,29 @@ bool pkgSourceList::Type::ParseStanza(vector<metaIndex *> &List,	/*{{{*/
    if (Enabled.empty() == false && StringToBool(Enabled) == false)
       return true;
 
-   std::map<char const * const, char const * const> mapping;
+   std::map<char const * const, std::pair<char const * const, bool> > mapping;
 #define APT_PLUSMINUS(X, Y) \
-   mapping.insert(std::make_pair(X, Y)); \
-   mapping.insert(std::make_pair(X "Add", Y "+")); \
-   mapping.insert(std::make_pair(X "Remove", Y "-"))
+   mapping.insert(std::make_pair(X, std::make_pair(Y, true))); \
+   mapping.insert(std::make_pair(X "Add", std::make_pair(Y "+", true))); \
+   mapping.insert(std::make_pair(X "Remove", std::make_pair(Y "-", true)))
    APT_PLUSMINUS("Architectures", "arch");
    APT_PLUSMINUS("Languages", "lang");
    APT_PLUSMINUS("Targets", "target");
 #undef APT_PLUSMINUS
-   mapping.insert(std::make_pair("Trusted", "trusted"));
-   mapping.insert(std::make_pair("Check-Valid-Until", "check-valid-until"));
-   mapping.insert(std::make_pair("Valid-Until-Min", "valid-until-min"));
-   mapping.insert(std::make_pair("Valid-Until-Max", "valid-until-max"));
+   mapping.insert(std::make_pair("Trusted", std::make_pair("trusted", false)));
+   mapping.insert(std::make_pair("Check-Valid-Until", std::make_pair("check-valid-until", false)));
+   mapping.insert(std::make_pair("Valid-Until-Min", std::make_pair("valid-until-min", false)));
+   mapping.insert(std::make_pair("Valid-Until-Max", std::make_pair("valid-until-max", false)));
+   mapping.insert(std::make_pair("Signed-By", std::make_pair("signed-by", false)));
 
-   for (std::map<char const * const, char const * const>::const_iterator m = mapping.begin(); m != mapping.end(); ++m)
+   for (std::map<char const * const, std::pair<char const * const, bool> >::const_iterator m = mapping.begin(); m != mapping.end(); ++m)
       if (Tags.Exists(m->first))
       {
-         // for deb822 the " " is the delimiter, but the backend expects ","
-         std::string option = Tags.FindS(m->first);
-         std::replace(option.begin(), option.end(), ' ', ',');
-         Options[m->second] = option;
+	 std::string option = Tags.FindS(m->first);
+	 // for deb822 the " " is the delimiter, but the backend expects ","
+	 if (m->second.second == true)
+	    std::replace(option.begin(), option.end(), ' ', ',');
+	 Options[m->second.first] = option;
       }
 
    // now create one item per suite/section

cmdline/apt-key.in

@@ -199,7 +199,7 @@ remove_key_from_keyring() {
 foreach_keyring_do() {
    local ACTION="$1"
    shift
-   # if a --keyring was given, just remove from there
+   # if a --keyring was given, just work on this one
    if [ -n "$FORCED_KEYRING" ]; then
 	$ACTION "$FORCED_KEYRING" "$@"
    else
@@ -279,7 +279,14 @@ merge_back_changes() {
 }
 
 setup_merged_keyring() {
-    if [ -z "$FORCED_KEYRING" ]; then
+    if [ -n "$FORCED_KEYID" ]; then
+	foreach_keyring_do 'import_keys_from_keyring' "${GPGHOMEDIR}/allrings.gpg"
+	FORCED_KEYRING="${GPGHOMEDIR}/forcedkeyid.gpg"
+	TRUSTEDFILE="${FORCED_KEYRING}"
+	GPG="$GPG --keyring $TRUSTEDFILE"
+	# ignore error as this "just" means we haven't found the forced keyid and the keyring will be empty
+	$GPG_CMD --batch --yes --keyring "${GPGHOMEDIR}/allrings.gpg" --export "$FORCED_KEYID" | $GPG --batch --yes --import || true
+    elif [ -z "$FORCED_KEYRING" ]; then
 	foreach_keyring_do 'import_keys_from_keyring' "${GPGHOMEDIR}/pubring.gpg"
 	if [ -r "${GPGHOMEDIR}/pubring.gpg" ]; then
 	    cp -a "${GPGHOMEDIR}/pubring.gpg" "${GPGHOMEDIR}/pubring.orig.gpg"
@@ -328,12 +335,17 @@ while [ -n "$1" ]; do
 	 TRUSTEDFILE="$1"
 	 FORCED_KEYRING="$1"
 	 ;;
+      --keyid)
+	 shift
+	 FORCED_KEYID="$1"
+	 ;;
       --secret-keyring)
 	 shift
 	 FORCED_SECRET_KEYRING="$1"
 	 ;;
       --readonly)
 	 merge_back_changes() { true; }
+	 create_new_keyring() { true; }
 	 ;;
       --fakeroot)
 	 requires_root() { true; }
@@ -460,7 +472,11 @@ case "$command" in
     verify)
 	setup_merged_keyring
 	if which gpgv >/dev/null 2>&1; then
-	    gpgv --homedir "${GPGHOMEDIR}" --keyring "${GPGHOMEDIR}/pubring.gpg" --ignore-time-conflict "$@"
+	    if [ -n "$FORCED_KEYRING" ]; then
+		gpgv --homedir "${GPGHOMEDIR}" --keyring "${FORCED_KEYRING}" --ignore-time-conflict "$@"
+	    else
+		gpgv --homedir "${GPGHOMEDIR}" --keyring "${GPGHOMEDIR}/pubring.gpg" --ignore-time-conflict "$@"
+	    fi
 	else
 	    $GPG --verify "$@"
 	fi

doc/sources.list.5.xml

@@ -232,18 +232,18 @@ deb-src [ option1=value1 option2=value2 ] uri suite [component1] [component2] [.
        anomalies.
 
        <itemizedlist>
-	  <listitem><para><option>Trusted</option> (<option>trusted</option>)
-		is a tri-state value which defaults to APT deciding if a source
-		is considered trusted or if warnings should be raised before e.g.
-		packages are installed from this source. This option can be used
-		to override this decision either with the value <literal>yes</literal>,
-		which lets APT consider this source always as a trusted source
-		even if it has no or fails authentication checks by disabling parts
-		of &apt-secure; and should therefore only be used in a local and trusted
-		context (if at all) as otherwise security is breached. The opposite
-		can be achieved with the value no, which causes the source to be handled
-		as untrusted even if the authentication checks passed successfully.
-		The default value can't be set explicitly.
+	  <listitem><para><option>Signed-By</option> (<option>signed-by</option>)
+		is either an absolute path to a keyring file (has to be
+		accessible and readable for the <literal>_apt</literal> user,
+		so ensure everyone has read-permissions on the file) or a
+		fingerprint of a key in either the
+		<filename>trusted.gpg</filename> keyring or in one of the
+		keyrings in the <filename>trusted.gpg.d/</filename> directory
+		(see <command>apt-key fingerprint</command>). If the option is
+		set only the key(s) in this keyring or only the key with this
+		fingerprint is used for the &apt-secure; verification of this
+		repository. Otherwise all keys in the trusted keyrings are
+		considered valid signers for this repository.
 	  </para></listitem>
 
 	  <listitem><para><option>Check-Valid-Until</option> (<option>check-valid-until</option>)

methods/gpgv.cc

@@ -37,13 +37,14 @@ class GPGVMethod : public pkgAcqMethod
 {
    private:
    string VerifyGetSigners(const char *file, const char *outfile,
-				vector<string> &GoodSigners, 
+				std::string const &key,
+				vector<string> &GoodSigners,
                                 vector<string> &BadSigners,
                                 vector<string> &WorthlessSigners,
 				vector<string> &NoPubKeySigners);
 
    protected:
-   virtual bool Fetch(FetchItem *Itm);
+   virtual bool URIAcquire(std::string const &Message, FetchItem *Itm);
    virtual bool Configuration(string Message);
    public:
 
@@ -61,6 +62,7 @@ bool GPGVMethod::Configuration(string Message)
 }
 
 string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
+					 std::string const &key,
 					 vector<string> &GoodSigners,
 					 vector<string> &BadSigners,
 					 vector<string> &WorthlessSigners,
@@ -80,7 +82,7 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
    if (pid < 0)
       return string("Couldn't spawn new process") + strerror(errno);
    else if (pid == 0)
-      ExecGPGV(outfile, file, 3, fd);
+      ExecGPGV(outfile, file, 3, fd, key);
    close(fd[1]);
 
    FILE *pipein = fdopen(fd[0], "r");
@@ -174,11 +176,11 @@ string GPGVMethod::VerifyGetSigners(const char *file, const char *outfile,
       return _("Unknown error executing apt-key");
 }
 
-bool GPGVMethod::Fetch(FetchItem *Itm)
+bool GPGVMethod::URIAcquire(std::string const &Message, FetchItem *Itm)
 {
-   URI Get = Itm->Uri;
-   string Path = Get.Host + Get.Path; // To account for relative paths
-   string keyID;
+   URI const Get = Itm->Uri;
+   string const Path = Get.Host + Get.Path; // To account for relative paths
+   std::string const key = LookupTag(Message, "Signed-By");
    vector<string> GoodSigners;
    vector<string> BadSigners;
    // a worthless signature is a expired or revoked one
@@ -190,7 +192,7 @@ bool GPGVMethod::Fetch(FetchItem *Itm)
    URIStart(Res);
 
    // Run apt-key on file, extract contents and get the key ID of the signer
-   string msg = VerifyGetSigners(Path.c_str(), Itm->DestFile.c_str(),
+   string msg = VerifyGetSigners(Path.c_str(), Itm->DestFile.c_str(), key,
                                  GoodSigners, BadSigners, WorthlessSigners,
                                  NoPubKeySigners);
    if (GoodSigners.empty() || !BadSigners.empty() || !NoPubKeySigners.empty())