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-rw-r--r--GPL-3674
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+ GNU GENERAL PUBLIC LICENSE
+ Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
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+
+ Preamble
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+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+ 17. Interpretation of Sections 15 and 16.
+
+ If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+ <program> Copyright (C) <year> <name of author>
+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+ The GNU General Public License does not permit incorporating your program
+into proprietary programs. If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License. But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..368c4dc
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,39 @@
+# Copyright (C) 2013 Timo Weingärtner <timo@tiwe.de>
+#
+# This file is part of ssh-agent-filter.
+#
+# ssh-agent-filter is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# ssh-agent-filter is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with ssh-agent-filter. If not, see <http://www.gnu.org/licenses/>.
+
+
+CXXFLAGS ?= -g -O2 -Wall -Wold-style-cast
+
+CXXFLAGS += -std=c++11
+LDFLAGS += -lboost_program_options -lboost_filesystem -lboost_system -lnettle
+
+all: ssh-agent-filter.1
+
+ssh-agent-filter.1: ssh-agent-filter
+ help2man -n $< -o $@ -N ./$<
+
+ssh-agent-filter: ssh-agent-filter.o
+
+ssh-agent-filter.o: ssh-agent-filter.C rfc4251.h ssh-agent.h version.h
+
+version.h:
+ test ! -d .git || git describe | sed 's/^.*$$/#define SSH_AGENT_FILTER_VERSION "ssh-agent-filter \0"/' > $@
+
+clean:
+ $(RM) ssh-agent-filter.1 ssh-agent-filter *.o
+
+.PHONY: version.h
diff --git a/rfc4251.h b/rfc4251.h
new file mode 100644
index 0000000..0a0a4ad
--- /dev/null
+++ b/rfc4251.h
@@ -0,0 +1,254 @@
+/*
+ * rfc4251.h -- implements types from RFC 4251, section 5
+ *
+ * rfc4251byte byte
+ * rfc4251bool bool
+ * rfc4251uint32 uint32
+ * rfc4251uint64 uint64
+ * rfc4251string string, incl. mpint and (without splitting) name-list
+ *
+ * those structs contain the objects in their RFC 4251 representation,
+ * conversions are provided via constructors and cast operators
+ *
+ * Copyright (C) 2013 Timo Weingärtner <timo@tiwe.de>
+ *
+ * This file is part of ssh-agent-filter.
+ *
+ * ssh-agent-filter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ssh-agent-filter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with ssh-agent-filter. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <vector>
+#include <string>
+#include <iostream>
+#include <arpa/inet.h> // ntohl() / htonl()
+#include <gmpxx.h>
+
+struct rfc4251byte {
+ union {
+ uint8_t value;
+ char buf[1];
+ };
+
+ rfc4251byte () = default;
+ rfc4251byte (rfc4251byte const &) = default;
+ rfc4251byte (rfc4251byte &&) = default;
+
+ inline explicit rfc4251byte (uint8_t v) : value(v) {}
+
+ rfc4251byte & operator= (rfc4251byte const &) = default;
+ rfc4251byte & operator= (rfc4251byte &&) = default;
+
+ inline operator uint8_t () const { return value; }
+};
+
+inline std::istream & operator>> (std::istream & is, rfc4251byte & x) {
+ return is.read(x.buf, sizeof(x.buf));
+}
+
+inline std::ostream & operator<< (std::ostream & os, rfc4251byte const & x) {
+ return os.write(x.buf, sizeof(x.buf));;
+}
+
+
+struct rfc4251bool {
+ union {
+ bool value;
+ char buf[1];
+ };
+
+ rfc4251bool () = default;
+ rfc4251bool (rfc4251bool const &) = default;
+ rfc4251bool (rfc4251bool &&) = default;
+
+ inline explicit rfc4251bool (uint8_t v) : value(v) {}
+
+ rfc4251bool & operator= (rfc4251bool const &) = default;
+ rfc4251bool & operator= (rfc4251bool &&) = default;
+
+ inline operator uint8_t () const { return value; }
+};
+
+inline std::istream & operator>> (std::istream & is, rfc4251bool & x) {
+ return is.read(x.buf, sizeof(x.buf));
+}
+
+inline std::ostream & operator<< (std::ostream & os, rfc4251bool const & x) {
+ return os.write(x.buf, sizeof(x.buf));;
+}
+
+
+struct rfc4251uint32 {
+ union {
+ uint32_t value;
+ char buf[4];
+ };
+
+ rfc4251uint32 () = default;
+ rfc4251uint32 (rfc4251uint32 const &) = default;
+ rfc4251uint32 (rfc4251uint32 &&) = default;
+
+ inline explicit rfc4251uint32 (uint32_t v) { value = htonl(v); }
+
+ rfc4251uint32 & operator= (rfc4251uint32 const &) = default;
+ rfc4251uint32 & operator= (rfc4251uint32 &&) = default;
+
+ inline operator uint32_t () const { return ntohl(value); }
+};
+
+inline std::istream & operator>> (std::istream & is, rfc4251uint32 & x) {
+ return is.read(x.buf, sizeof(x.buf));
+}
+
+inline std::ostream & operator<< (std::ostream & os, rfc4251uint32 const & x) {
+ return os.write(x.buf, sizeof(x.buf));;
+}
+
+
+struct rfc4251uint64 {
+ union {
+ uint64_t value;
+ char buf[8];
+ };
+
+ rfc4251uint64 () = default;
+ rfc4251uint64 (rfc4251uint64 const &) = default;
+ rfc4251uint64 (rfc4251uint64 &&) = default;
+
+ inline explicit rfc4251uint64 (uint64_t v);
+
+ rfc4251uint64 & operator= (rfc4251uint64 const &) = default;
+ rfc4251uint64 & operator= (rfc4251uint64 &&) = default;
+
+ inline explicit operator uint64_t () const;
+};
+
+inline rfc4251uint64::rfc4251uint64 (uint64_t v) {
+ for (int_fast8_t i = 7; i >= 0; --i) {
+ buf[i] = v & 0xff;
+ v >>= 8;
+ }
+}
+
+inline rfc4251uint64::operator uint64_t () const {
+ uint64_t ret{0};
+ for (uint_fast8_t i = 0; i < 8; ++i) {
+ ret |= buf[i];
+ ret <<= 8;
+ }
+ return ret;
+}
+
+inline std::istream & operator>> (std::istream & is, rfc4251uint64 & x) {
+ return is.read(x.buf, sizeof(x.buf));
+}
+
+inline std::ostream & operator<< (std::ostream & os, rfc4251uint64 const & x) {
+ return os.write(x.buf, sizeof(x.buf));;
+}
+
+
+struct rfc4251string {
+ std::vector<char> value;
+
+ rfc4251string () = default;
+ rfc4251string (rfc4251string const &) = default;
+ rfc4251string (rfc4251string &&) = default;
+
+ inline explicit rfc4251string (char const *);
+ inline explicit rfc4251string (char const *, size_t);
+ inline explicit rfc4251string (std::string const & s) : rfc4251string{s.data(), s.size()} {}
+ inline explicit rfc4251string (mpz_srcptr);
+ inline explicit rfc4251string (mpz_class const & x) : rfc4251string{x.get_mpz_t()} {}
+
+ rfc4251string & operator= (rfc4251string const &) = default;
+ rfc4251string & operator= (rfc4251string &&) = default;
+
+ inline operator std::string () const;
+ inline operator mpz_class () const;
+};
+
+inline rfc4251string::rfc4251string (char const * s) {
+ auto len = ntohl(*reinterpret_cast<uint32_t const *>(s));
+ value.insert(value.begin(), s, s + 4 + len);
+}
+
+inline rfc4251string::rfc4251string (char const * s, size_t l) {
+ rfc4251uint32 tmp(l);
+ value.insert(value.end(), std::begin(tmp.buf), std::end(tmp.buf));
+ value.insert(value.end(), s, s + l);
+}
+
+inline rfc4251string::rfc4251string (mpz_srcptr x) {
+ if (mpz_sgn(x) == 0)
+ value.assign(4, 0);
+ else if (mpz_sgn(x) == 1) {
+ ssize_t bits = mpz_sizeinbase(x, 2);
+ ssize_t bytes = (bits + 7) / 8;
+ ssize_t extrabyte = bits % 8 ? 0 : 1; // need extra byte if MSB is 1 to keep it non-negative
+ value.resize(4 + bytes + extrabyte);
+ *reinterpret_cast<uint32_t *>(value.data()) = htonl(bytes + extrabyte);
+ value[4] = 0;
+ mpz_export(value.data() + 4 + extrabyte, nullptr, 1, 1, 1, 0, x);
+ } else {
+ mpz_class tmp(x);
+ tmp += 1;
+ x = tmp.get_mpz_t();
+ ssize_t bits = mpz_sizeinbase(x, 2);
+ ssize_t bytes = (bits + 7) / 8;
+ ssize_t extrabyte = bits % 8 ? 0 : 1; // need extra byte if MSB is 1 (0 after ^= below) to keep it negative
+ value.resize(4 + bytes + extrabyte);
+ *reinterpret_cast<uint32_t *>(value.data()) = htonl(bytes + extrabyte);
+ value[4] = 0;
+ mpz_export(value.data() + 4 + extrabyte, nullptr, 1, 1, 1, 0, x);
+ for (auto i = value.data() + 4; i < value.data() + value.size(); ++i)
+ *i ^= 0xff;
+ }
+}
+
+inline rfc4251string::operator std::string () const {
+ return std::string(value.begin() + 4, value.end());
+}
+
+inline rfc4251string::operator mpz_class () const {
+ mpz_class ret;
+ mpz_import(ret.get_mpz_t(), value.size() - 4, 1, 1, 1, 0, value.data() + 4);
+ if (mpz_sizeinbase(ret.get_mpz_t(), 2) == (value.size() - 4) * 8) { // negative
+ mpz_com(ret.get_mpz_t(), ret.get_mpz_t());
+ ret += 1;
+ mpz_neg(ret.get_mpz_t(), ret.get_mpz_t());
+ }
+ return ret;
+}
+
+inline std::istream & operator>> (std::istream & is, rfc4251string & s) {
+ s.value.resize(4);
+ if (is.read(s.value.data(), 4)) {
+ auto len = ntohl(*reinterpret_cast<uint32_t const *>(s.value.data()));
+ s.value.resize(4 + len);
+ is.read(s.value.data() + 4, len);
+ }
+ return is;
+}
+
+inline std::ostream & operator<< (std::ostream & os, rfc4251string const & s) {
+ return os.write(s.value.data(), s.value.size());
+}
+
+inline bool operator== (rfc4251string const & l, rfc4251string const & r) {
+ return l.value == r.value;
+}
+
+inline bool operator< (rfc4251string const & l, rfc4251string const & r) {
+ return l.value < r.value;
+}
diff --git a/ssh-agent-filter.C b/ssh-agent-filter.C
new file mode 100644
index 0000000..5aa086b
--- /dev/null
+++ b/ssh-agent-filter.C
@@ -0,0 +1,378 @@
+/*
+ * ssh-agent-filter.C -- filtering proxy for ssh-agent meant to be forwarded to untrusted servers
+ *
+ * Copyright (C) 2013 Timo Weingärtner <timo@tiwe.de>
+ *
+ * This file is part of ssh-agent-filter.
+ *
+ * ssh-agent-filter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ssh-agent-filter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with ssh-agent-filter. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <boost/program_options.hpp>
+namespace po = boost::program_options;
+
+#include <boost/filesystem.hpp>
+namespace fs = boost::filesystem;
+
+#include <string>
+#include <vector>
+#include <set>
+#include <iostream>
+#include <sstream>
+#include <stdexcept>
+#include <thread>
+#include <ext/stdio_filebuf.h>
+
+#include <csignal>
+#include <cstdlib>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sysexits.h>
+#include <nettle/md5.h>
+#include <nettle/base64.h>
+#include <nettle/base16.h>
+
+#include "rfc4251.h"
+#include "ssh-agent.h"
+#include "version.h"
+
+
+std::vector<std::string> allowed_b64;
+std::vector<std::string> allowed_md5;
+std::vector<std::string> allowed_comment;
+std::set<rfc4251string> allowed_pubkeys;
+bool debug{false};
+fs::path path;
+
+
+std::string md5_hex (std::string const & s) {
+ struct md5_ctx ctx;
+ md5_init(&ctx);
+ md5_update(&ctx, s.size(), reinterpret_cast<uint8_t const *>(s.data()));
+ uint8_t bin[MD5_DIGEST_SIZE];
+ md5_digest(&ctx, MD5_DIGEST_SIZE, bin);
+ uint8_t hex[BASE16_ENCODE_LENGTH(MD5_DIGEST_SIZE)];
+ base16_encode_update(hex, MD5_DIGEST_SIZE, bin);
+ return std::string(reinterpret_cast<char const *>(hex), sizeof(hex));
+}
+
+std::string base64_encode (std::string const & s) {
+ struct base64_encode_ctx ctx;
+ base64_encode_init(&ctx);
+ uint8_t b64[BASE64_ENCODE_LENGTH(s.size())];
+ auto len = base64_encode_update(&ctx, b64, s.size(), reinterpret_cast<uint8_t const *>(s.data()));
+ len += base64_encode_final(&ctx, b64 + len);
+ return std::string(reinterpret_cast<char const *>(b64), len);
+}
+
+int make_upstream_agent_conn () {
+ char const * path;
+ int sock;
+ struct sockaddr_un addr;
+
+ if (!(path = getenv("SSH_AUTH_SOCK"))) {
+ std::clog << "no $SSH_AUTH_SOCK" << std::endl;
+ exit(EX_UNAVAILABLE);
+ }
+
+ if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
+ perror("socket");
+ exit(EX_UNAVAILABLE);
+ }
+
+ addr.sun_family = AF_UNIX;
+
+ if (strlen(path) >= sizeof(addr.sun_path)) {
+ std::clog << "$SSH_AUTH_SOCK too long" << std::endl;
+ exit(EX_UNAVAILABLE);
+ }
+
+ strcpy(addr.sun_path, path);
+
+ if (connect(sock, reinterpret_cast<struct sockaddr const *>(&addr), sizeof(addr))) {
+ perror("connect");
+ exit(EX_UNAVAILABLE);
+ }
+
+ return sock;
+}
+
+int make_listen_sock () {
+ int sock;
+ struct sockaddr_un addr;
+
+ if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
+ perror("socket");
+ exit(EX_UNAVAILABLE);
+ }
+
+ addr.sun_family = AF_UNIX;
+
+ if (path.native().length() >= sizeof(addr.sun_path)) {
+ std::clog << "path for listen socket too long" << std::endl;
+ exit(EX_UNAVAILABLE);
+ }
+
+ strcpy(addr.sun_path, path.c_str());
+
+ if (bind(sock, reinterpret_cast<struct sockaddr const *>(&addr), sizeof(addr))) {
+ perror("bind");
+ exit(EX_UNAVAILABLE);
+ }
+
+ if (listen(sock, 0)) {
+ perror("listen");
+ exit(EX_UNAVAILABLE);
+ }
+
+ return sock;
+}
+
+void parse_cmdline (int const argc, char const * const * const argv) {
+ po::options_description opts("OPTIONS");
+ opts.add_options()
+ ("comment,c", po::value(&allowed_comment), "key specified by comment")
+ ("debug,d", po::bool_switch(&debug), "show even more stuff")
+ ("fingerprint,fp,f", po::value(&allowed_md5), "key specified by pubkey's hex-encoded md5 fingerprint")
+ ("help,h", "print this help message")
+ ("key,k", po::value(&allowed_b64), "key specified by base64-encoded pubkey")
+ ("version,V", "print version information")
+ ;
+ po::variables_map config;
+ po::store(po::parse_command_line(argc, argv, opts), config);
+ po::notify(config);
+
+ if (config.count("help")) {
+ std::cout << "Invocation: ssh-agent-filter [ OPTIONS ] -- [ SSH ARGUMENTS ]" << std::endl;
+ std::cout << opts << std::endl;
+ exit(EX_OK);
+ }
+
+ if (config.count("version")) {
+ std::cout << SSH_AGENT_FILTER_VERSION << std::endl;
+ exit(EX_OK);
+ }
+
+ // canonicalize hashes
+ for (auto & s : allowed_md5)
+ for (auto it = s.begin(); it != s.end(); )
+ if (isxdigit(*it)) {
+ *it = tolower(*it);
+ ++it;
+ } else
+ it = s.erase(it);
+}
+
+void setup_filters () {
+ __gnu_cxx::stdio_filebuf<char> agent_filebuf(make_upstream_agent_conn(), std::ios::in | std::ios::out);
+ std::iostream agent(&agent_filebuf);
+ agent.exceptions(std::ios::badbit | std::ios::failbit);
+
+ agent << rfc4251string(std::string(1, SSH2_AGENTC_REQUEST_IDENTITIES));
+ rfc4251string answer;
+ agent >> answer;
+ std::istringstream answer_iss(answer);
+ answer_iss.exceptions(std::ios::badbit | std::ios::failbit);
+ rfc4251byte resp_code;
+ answer_iss >> resp_code;
+ if (resp_code != SSH2_AGENT_IDENTITIES_ANSWER)
+ throw std::runtime_error("unexpected answer from ssh-agent");
+ rfc4251uint32 keycount;
+ answer_iss >> keycount;
+ for (uint32_t i = keycount; i; --i) {
+ rfc4251string key;
+ rfc4251string comment;
+ answer_iss >> key >> comment;
+
+ auto b64 = base64_encode(key);
+ if (debug) std::clog << b64 << std::endl;
+
+ auto md5 = md5_hex(key);
+ if (debug) std::clog << md5 << std::endl;
+
+ std::string comm(comment);
+ if (debug) std::clog << comm << std::endl;
+
+ if (std::count(allowed_b64.begin(), allowed_b64.end(), b64)) {
+ allowed_pubkeys.insert(key);
+ if (debug) std::clog << "key allowed by equal base64 representation" << std::endl;
+ }
+ if (std::count(allowed_md5.begin(), allowed_md5.end(), md5)) {
+ allowed_pubkeys.insert(key);
+ if (debug) std::clog << "key allowed by matching md5 fingerprint" << std::endl;
+ }
+ if (std::count(allowed_comment.begin(), allowed_comment.end(), comm)) {
+ allowed_pubkeys.insert(key);
+ if (debug) std::clog << "key allowed by matching comment" << std::endl;
+ }
+
+ if (debug) std::clog << std::endl;
+ }
+}
+
+rfc4251string handle_request (rfc4251string const & r) {
+ std::istringstream request(r);
+ std::ostringstream answer;
+ request.exceptions(std::ios::badbit | std::ios::failbit);
+ answer.exceptions(std::ios::badbit | std::ios::failbit);
+ rfc4251byte request_code;
+ request >> request_code;
+ switch (request_code) {
+ case SSH2_AGENTC_REQUEST_IDENTITIES:
+ {
+ __gnu_cxx::stdio_filebuf<char> agent_filebuf(make_upstream_agent_conn(), std::ios::in | std::ios::out);
+ std::iostream agent(&agent_filebuf);
+ agent.exceptions(std::ios::badbit | std::ios::failbit);
+ rfc4251string agent_answer;
+ agent << rfc4251string(std::string(1, SSH2_AGENTC_REQUEST_IDENTITIES));
+ agent >> agent_answer;
+ // temp to test key filtering when signing
+ //return agent_answer;
+ std::istringstream agent_answer_iss(agent_answer);
+ rfc4251byte answer_code;
+ rfc4251uint32 keycount;
+ agent_answer_iss >> answer_code >> keycount;
+ if (answer_code != SSH2_AGENT_IDENTITIES_ANSWER)
+ throw std::runtime_error("unexpected answer from ssh-agent");
+ std::vector<std::pair<rfc4251string, rfc4251string>> keys;
+ for (uint32_t i = keycount; i; --i) {
+ rfc4251string key;
+ rfc4251string comment;
+ agent_answer_iss >> key >> comment;
+ if (allowed_pubkeys.count(key))
+ keys.emplace_back(std::move(key), std::move(comment));
+ }
+ answer << answer_code << rfc4251uint32(keys.size());
+ for (auto const & k : keys)
+ answer << k.first << k.second;
+ }
+ break;
+ case SSH2_AGENTC_SIGN_REQUEST:
+ {
+ rfc4251string key;
+ request >> key;
+ if (allowed_pubkeys.count(key)) {
+ __gnu_cxx::stdio_filebuf<char> agent_filebuf(make_upstream_agent_conn(), std::ios::in | std::ios::out);
+ std::iostream agent(&agent_filebuf);
+ agent.exceptions(std::ios::badbit | std::ios::failbit);
+ rfc4251string agent_answer;
+
+ agent << r;
+ agent >> agent_answer;
+ return agent_answer;
+ } else
+ answer << rfc4251byte(SSH_AGENT_FAILURE);
+ }
+ break;
+ case SSH_AGENTC_REQUEST_RSA_IDENTITIES:
+ answer << rfc4251byte(SSH_AGENT_RSA_IDENTITIES_ANSWER);
+ // we got no SSHv1 keys
+ answer << rfc4251uint32(0);
+ break;
+ case SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES:
+ answer << rfc4251byte(SSH_AGENT_SUCCESS);
+ break;
+ case SSH_AGENTC_RSA_CHALLENGE:
+ case SSH_AGENTC_ADD_RSA_IDENTITY:
+ case SSH_AGENTC_REMOVE_RSA_IDENTITY:
+ case SSH_AGENTC_ADD_RSA_ID_CONSTRAINED:
+ case SSH2_AGENTC_ADD_IDENTITY:
+ case SSH2_AGENTC_REMOVE_IDENTITY:
+ case SSH2_AGENTC_REMOVE_ALL_IDENTITIES:
+ case SSH2_AGENTC_ADD_ID_CONSTRAINED:
+ case SSH_AGENTC_ADD_SMARTCARD_KEY:
+ case SSH_AGENTC_REMOVE_SMARTCARD_KEY:
+ case SSH_AGENTC_LOCK:
+ case SSH_AGENTC_UNLOCK:
+ case SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED:
+ default:
+ answer << rfc4251byte(SSH_AGENT_FAILURE);
+ break;
+ }
+
+ return rfc4251string(answer.str());
+}
+
+void handle_client (int const sock) {
+ // we could use only one streambuf and iostream but when
+ // switching from read to write an lseek call is made that
+ // fails with ESPIPE and causes an exception
+ __gnu_cxx::stdio_filebuf<char> client_filebuf_in(sock, std::ios::in);
+ __gnu_cxx::stdio_filebuf<char> client_filebuf_out(sock, std::ios::out);
+ std::istream client_in(&client_filebuf_in);
+ std::ostream client_out(&client_filebuf_out);
+ client_out.exceptions(std::ios::badbit | std::ios::failbit);
+
+ rfc4251string request;
+ while (client_in >> request) try {
+ client_out << handle_request(request) << std::flush;
+ } catch (...) {
+ break;
+ }
+}
+
+void sighandler (int sig) {
+ switch (sig) {
+ case SIGINT:
+ case SIGPIPE:
+ break;
+ default:
+ remove(path);
+ std::abort();
+ }
+}
+
+int main (int const argc, char const * const * const argv) {
+ parse_cmdline(argc, argv);
+
+ setup_filters();
+
+ path = fs::current_path() / ("agent." + std::to_string(getpid()));
+ int listen_sock = make_listen_sock();
+
+ if (not debug) {
+ pid_t pid = fork();
+ if (pid == -1) {
+ perror("fork");
+ exit(EX_OSERR);
+ }
+ if (pid > 0) {
+ std::cout << "SSH_AUTH_SOCK='" << path << "'; export SSH_AUTH_SOCK;" << std::endl;
+ std::cout << "SSH_AGENT_PID='" << pid << "'; export SSH_AGENT_PID;" << std::endl;
+ std::cout << "echo 'Agent pid " << pid << "';" << std::endl;
+ exit(EX_OK);
+ }
+
+ setsid();
+ chdir("/");
+ int devnull = open("/dev/null", O_RDWR);
+ dup2(devnull, 0);
+ dup2(devnull, 1);
+ dup2(devnull, 2);
+ close(devnull);
+
+ signal(SIGINT, sighandler);
+ signal(SIGPIPE, sighandler);
+ signal(SIGHUP, sighandler);
+ signal(SIGTERM, sighandler);
+ }
+
+ int client_sock;
+ while ((client_sock = accept(listen_sock, nullptr, nullptr)) != -1) {
+ std::thread t(handle_client, client_sock);
+ t.detach();
+ }
+}
diff --git a/ssh-agent.h b/ssh-agent.h
new file mode 100644
index 0000000..7824dc5
--- /dev/null
+++ b/ssh-agent.h
@@ -0,0 +1,55 @@
+/*
+ * ssh-agent.h
+ *
+ * constants copied from http://api.libssh.org/rfc/PROTOCOL.agent
+ *
+ * public domain.
+ */
+
+// 3. Protocol message numbers
+
+// 3.1 Requests from client to agent for protocol 1 key operations
+
+#define SSH_AGENTC_REQUEST_RSA_IDENTITIES 1
+#define SSH_AGENTC_RSA_CHALLENGE 3
+#define SSH_AGENTC_ADD_RSA_IDENTITY 7
+#define SSH_AGENTC_REMOVE_RSA_IDENTITY 8
+#define SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES 9
+#define SSH_AGENTC_ADD_RSA_ID_CONSTRAINED 24
+
+// 3.2 Requests from client to agent for protocol 2 key operations
+
+#define SSH2_AGENTC_REQUEST_IDENTITIES 11
+#define SSH2_AGENTC_SIGN_REQUEST 13
+#define SSH2_AGENTC_ADD_IDENTITY 17
+#define SSH2_AGENTC_REMOVE_IDENTITY 18
+#define SSH2_AGENTC_REMOVE_ALL_IDENTITIES 19
+#define SSH2_AGENTC_ADD_ID_CONSTRAINED 25
+
+// 3.3 Key-type independent requests from client to agent
+
+#define SSH_AGENTC_ADD_SMARTCARD_KEY 20
+#define SSH_AGENTC_REMOVE_SMARTCARD_KEY 21
+#define SSH_AGENTC_LOCK 22
+#define SSH_AGENTC_UNLOCK 23
+#define SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED 26
+
+// 3.4 Generic replies from agent to client
+
+#define SSH_AGENT_FAILURE 5
+#define SSH_AGENT_SUCCESS 6
+
+// 3.5 Replies from agent to client for protocol 1 key operations
+
+#define SSH_AGENT_RSA_IDENTITIES_ANSWER 2
+#define SSH_AGENT_RSA_RESPONSE 4
+
+// 3.6 Replies from agent to client for protocol 2 key operations
+
+#define SSH2_AGENT_IDENTITIES_ANSWER 12
+#define SSH2_AGENT_SIGN_RESPONSE 14
+
+// 3.7 Key constraint identifiers
+
+#define SSH_AGENT_CONSTRAIN_LIFETIME 1
+#define SSH_AGENT_CONSTRAIN_CONFIRM 2