rpc: Implement random-cookie based authentication

When no `-rpcpassword` is specified, use a special 'cookie' file for
authentication. This file is generated with random content when the
daemon starts, and deleted when it exits. Read access to this file
controls who can access through RPC. By default this file is stored in
the data directory but it be overriden with `-rpccookiefile`.

This is similar to Tor CookieAuthentication: see
https://www.torproject.org/docs/tor-manual.html.en

Alternative to #6258. Like that pull, this allows running bitcoind
without any manual configuration. However, daemons should ideally never write to
their configuration files, so I prefer this solution.

1 files changed, 67 insertions, 0 deletions

diff --git a/src/rpcprotocol.cpp b/src/rpcprotocol.cpp
index 89dec2977e..2e5c913734 100644
--- a/src/rpcprotocol.cpp
+++ b/src/rpcprotocol.cpp
@@ -6,6 +6,7 @@
 #include "rpcprotocol.h"
 
 #include "clientversion.h"
+#include "random.h"
 #include "tinyformat.h"
 #include "util.h"
 #include "utilstrencodings.h"
@@ -13,6 +14,7 @@
 #include "version.h"
 
 #include <stdint.h>
+#include <fstream>
 
 #include <boost/algorithm/string.hpp>
 #include <boost/asio.hpp>
@@ -287,3 +289,68 @@ UniValue JSONRPCError(int code, const string& message)
     error.push_back(Pair("message", message));
     return error;
 }
+
+/** Username used when cookie authentication is in use (arbitrary, only for
+ * recognizability in debugging/logging purposes)
+ */
+static const std::string COOKIEAUTH_USER = "__cookie__";
+/** Default name for auth cookie file */
+static const std::string COOKIEAUTH_FILE = ".cookie";
+
+boost::filesystem::path GetAuthCookieFile()
+{
+    boost::filesystem::path path(GetArg("-rpccookiefile", COOKIEAUTH_FILE));
+    if (!path.is_complete()) path = GetDataDir() / path;
+    return path;
+}
+
+bool GenerateAuthCookie(std::string *cookie_out)
+{
+    unsigned char rand_pwd[32];
+    GetRandBytes(rand_pwd, 32);
+    std::string cookie = COOKIEAUTH_USER + ":" + EncodeBase64(&rand_pwd[0],32);
+
+    /** the umask determines what permissions are used to create this file -
+     * these are set to 077 in init.cpp unless overridden with -sysperms.
+     */
+    std::ofstream file;
+    boost::filesystem::path filepath = GetAuthCookieFile();
+    file.open(filepath.string().c_str());
+    if (!file.is_open()) {
+        LogPrintf("Unable to open cookie authentication file %s for writing\n", filepath.string());
+        return false;
+    }
+    file << cookie;
+    file.close();
+    LogPrintf("Generated RPC authentication cookie %s\n", filepath.string());
+
+    if (cookie_out)
+        *cookie_out = cookie;
+    return true;
+}
+
+bool GetAuthCookie(std::string *cookie_out)
+{
+    std::ifstream file;
+    std::string cookie;
+    boost::filesystem::path filepath = GetAuthCookieFile();
+    file.open(filepath.string().c_str());
+    if (!file.is_open())
+        return false;
+    std::getline(file, cookie);
+    file.close();
+
+    if (cookie_out)
+        *cookie_out = cookie;
+    return true;
+}
+
+void DeleteAuthCookie()
+{
+    try {
+        boost::filesystem::remove(GetAuthCookieFile());
+    } catch (const boost::filesystem::filesystem_error& e) {
+        LogPrintf("%s: Unable to remove random auth cookie file: %s\n", __func__, e.what());
+    }
+}
+