init: add option for rpccookie permissions

Add a bitcoind launch option `-rpccookieperms` to configure the file
permissions of the cookie on Unix systems.

Author: willcl-ark

src/httprpc.cpp

@@ -11,6 +11,8 @@
 #include <netaddress.h>
 #include <rpc/protocol.h>
 #include <rpc/server.h>
+#include <util/fs.h>
+#include <util/fs_helpers.h>
 #include <util/strencodings.h>
 #include <util/string.h>
 #include <walletinitinterface.h>
@@ -19,6 +21,7 @@
 #include <iterator>
 #include <map>
 #include <memory>
+#include <optional>
 #include <set>
 #include <string>
 #include <vector>
@@ -244,8 +247,20 @@ static bool InitRPCAuthentication()
 {
     if (gArgs.GetArg("-rpcpassword", "") == "")
     {
-        LogPrintf("Using random cookie authentication.\n");
-        if (!GenerateAuthCookie(&strRPCUserColonPass)) {
+        LogInfo("Using random cookie authentication.\n");
+
+        std::optional<fs::perms> cookie_perms{std::nullopt};
+        auto cookie_perms_arg{gArgs.GetArg("-rpccookieperms")};
+        if (cookie_perms_arg) {
+            auto perm_opt = InterpretPermString(*cookie_perms_arg);
+            if (!perm_opt) {
+                LogInfo("Invalid -rpccookieperms=%s; must be one of 'owner', 'group', or 'all'.\n", *cookie_perms_arg);
+                return false;
+            }
+            cookie_perms = *perm_opt;
+        }
+
+        if (!GenerateAuthCookie(&strRPCUserColonPass, cookie_perms)) {
             return false;
         }
     } else {

src/init.cpp

@@ -650,6 +650,7 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-rpcbind=<addr>[:port]", "Bind to given address to listen for JSON-RPC connections. Do not expose the RPC server to untrusted networks such as the public internet! This option is ignored unless -rpcallowip is also passed. Port is optional and overrides -rpcport. Use [host]:port notation for IPv6. This option can be specified multiple times (default: 127.0.0.1 and ::1 i.e., localhost)", ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::RPC);
     argsman.AddArg("-rpcdoccheck", strprintf("Throw a non-fatal error at runtime if the documentation for an RPC is incorrect (default: %u)", DEFAULT_RPC_DOC_CHECK), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::RPC);
     argsman.AddArg("-rpccookiefile=<loc>", "Location of the auth cookie. Relative paths will be prefixed by a net-specific datadir location. (default: data dir)", ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
+    argsman.AddArg("-rpccookieperms=<readable-by>", strprintf("Set permissions on the RPC auth cookie file so that it is readable by [owner|group|all] (default: owner [via umask 0077])"), ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
     argsman.AddArg("-rpcpassword=<pw>", "Password for JSON-RPC connections", ArgsManager::ALLOW_ANY | ArgsManager::SENSITIVE, OptionsCategory::RPC);
     argsman.AddArg("-rpcport=<port>", strprintf("Listen for JSON-RPC connections on <port> (default: %u, testnet: %u, signet: %u, regtest: %u)", defaultBaseParams->RPCPort(), testnetBaseParams->RPCPort(), signetBaseParams->RPCPort(), regtestBaseParams->RPCPort()), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::RPC);
     argsman.AddArg("-rpcservertimeout=<n>", strprintf("Timeout during HTTP requests (default: %d)", DEFAULT_HTTP_SERVER_TIMEOUT), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::RPC);

src/rpc/request.cpp

@@ -5,12 +5,11 @@
 
 #include <rpc/request.h>
 
-#include <util/fs.h>
-
 #include <common/args.h>
 #include <logging.h>
 #include <random.h>
 #include <rpc/protocol.h>
+#include <util/fs.h>
 #include <util/fs_helpers.h>
 #include <util/strencodings.h>
 
@@ -82,7 +81,7 @@ static fs::path GetAuthCookieFile(bool temp=false)
 
 static bool g_generated_cookie = false;
 
-bool GenerateAuthCookie(std::string *cookie_out)
+bool GenerateAuthCookie(std::string* cookie_out, std::optional<fs::perms> cookie_perms)
 {
     const size_t COOKIE_SIZE = 32;
     unsigned char rand_pwd[COOKIE_SIZE];
@@ -96,19 +95,29 @@ bool GenerateAuthCookie(std::string *cookie_out)
     fs::path filepath_tmp = GetAuthCookieFile(true);
     file.open(filepath_tmp);
     if (!file.is_open()) {
-        LogPrintf("Unable to open cookie authentication file %s for writing\n", fs::PathToString(filepath_tmp));
+        LogInfo("Unable to open cookie authentication file %s for writing\n", fs::PathToString(filepath_tmp));
         return false;
     }
     file << cookie;
     file.close();
 
     fs::path filepath = GetAuthCookieFile(false);
     if (!RenameOver(filepath_tmp, filepath)) {
-        LogPrintf("Unable to rename cookie authentication file %s to %s\n", fs::PathToString(filepath_tmp), fs::PathToString(filepath));
+        LogInfo("Unable to rename cookie authentication file %s to %s\n", fs::PathToString(filepath_tmp), fs::PathToString(filepath));
         return false;
     }
+    if (cookie_perms) {
+        std::error_code code;
+        fs::permissions(filepath, cookie_perms.value(), fs::perm_options::replace, code);
+        if (code) {
+            LogInfo("Unable to set permissions on cookie authentication file %s\n", fs::PathToString(filepath_tmp));
+            return false;
+        }
+    }
+
     g_generated_cookie = true;
-    LogPrintf("Generated RPC authentication cookie %s\n", fs::PathToString(filepath));
+    LogInfo("Generated RPC authentication cookie %s\n", fs::PathToString(filepath));
+    LogInfo("Permissions used for cookie: %s\n", PermsToSymbolicString(fs::status(filepath).permissions()));
 
     if (cookie_out)
         *cookie_out = cookie;

src/rpc/request.h

@@ -7,17 +7,19 @@
 #define BITCOIN_RPC_REQUEST_H
 
 #include <any>
+#include <optional>
 #include <string>
 
 #include <univalue.h>
+#include <util/fs.h>
 
 UniValue JSONRPCRequestObj(const std::string& strMethod, const UniValue& params, const UniValue& id);
 UniValue JSONRPCReplyObj(const UniValue& result, const UniValue& error, const UniValue& id);
 std::string JSONRPCReply(const UniValue& result, const UniValue& error, const UniValue& id);
 UniValue JSONRPCError(int code, const std::string& message);
 
 /** Generate a new RPC authentication cookie and write it to disk */
-bool GenerateAuthCookie(std::string *cookie_out);
+bool GenerateAuthCookie(std::string* cookie_out, std::optional<fs::perms> cookie_perms=std::nullopt);
 /** Read the RPC authentication cookie from disk */
 bool GetAuthCookie(std::string *cookie_out);
 /** Delete RPC authentication cookie from disk */