lix/src/nix/daemon.cc
Robert Hensing fd4f03b8fd
Merge pull request #8519 from fricklerhandwerk/reword-trusted-users
reword documentation on trusted users and substituters
2023-06-23 13:08:46 +02:00

524 lines
16 KiB
C++

///@file
#include "command.hh"
#include "shared.hh"
#include "local-store.hh"
#include "remote-store.hh"
#include "remote-store-connection.hh"
#include "util.hh"
#include "serialise.hh"
#include "archive.hh"
#include "globals.hh"
#include "derivations.hh"
#include "finally.hh"
#include "legacy.hh"
#include "daemon.hh"
#include <algorithm>
#include <climits>
#include <cstring>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <errno.h>
#include <pwd.h>
#include <grp.h>
#include <fcntl.h>
#if __APPLE__ || __FreeBSD__
#include <sys/ucred.h>
#endif
using namespace nix;
using namespace nix::daemon;
/**
* Settings related to authenticating clients for the Nix daemon.
*
* For pipes we have little good information about the client side, but
* for Unix domain sockets we do. So currently these options implemented
* mandatory access control based on user names and group names (looked
* up and translated to UID/GIDs in the CLI process that runs the code
* in this file).
*
* No code outside of this file knows about these settings (this is not
* exposed in a header); all authentication and authorization happens in
* `daemon.cc`.
*/
struct AuthorizationSettings : Config {
Setting<Strings> trustedUsers{
this, {"root"}, "trusted-users",
R"(
A list of user names, separated by whitespace.
These users will have additional rights when connecting to the Nix daemon, such as the ability to specify additional [substituters](#conf-substituters), or to import unsigned [NARs](@docroot@/glossary.md#gloss-nar).
You can also specify groups by prefixing names with `@`.
For instance, `@wheel` means all users in the `wheel` group.
> **Warning**
>
> Adding a user to `trusted-users` is essentially equivalent to giving that user root access to the system.
> For example, the user can access or replace store path contents that are critical for system security.
)"};
/**
* Who we trust to use the daemon in safe ways
*/
Setting<Strings> allowedUsers{
this, {"*"}, "allowed-users",
R"(
A list user names, separated by whitespace.
These users are allowed to connect to the Nix daemon.
You can specify groups by prefixing names with `@`.
For instance, `@wheel` means all users in the `wheel` group.
Also, you can allow all users by specifying `*`.
> **Note**
>
> Trusted users (set in [`trusted-users`](#conf-trusted-users)) can always connect to the Nix daemon.
)"};
};
AuthorizationSettings authorizationSettings;
static GlobalConfig::Register rSettings(&authorizationSettings);
#ifndef __linux__
#define SPLICE_F_MOVE 0
static ssize_t splice(int fd_in, void *off_in, int fd_out, void *off_out, size_t len, unsigned int flags)
{
// We ignore most parameters, we just have them for conformance with the linux syscall
std::vector<char> buf(8192);
auto read_count = read(fd_in, buf.data(), buf.size());
if (read_count == -1)
return read_count;
auto write_count = decltype(read_count)(0);
while (write_count < read_count) {
auto res = write(fd_out, buf.data() + write_count, read_count - write_count);
if (res == -1)
return res;
write_count += res;
}
return read_count;
}
#endif
static void sigChldHandler(int sigNo)
{
// Ensure we don't modify errno of whatever we've interrupted
auto saved_errno = errno;
// Reap all dead children.
while (waitpid(-1, 0, WNOHANG) > 0) ;
errno = saved_errno;
}
static void setSigChldAction(bool autoReap)
{
struct sigaction act, oact;
act.sa_handler = autoReap ? sigChldHandler : SIG_DFL;
sigfillset(&act.sa_mask);
act.sa_flags = 0;
if (sigaction(SIGCHLD, &act, &oact))
throw SysError("setting SIGCHLD handler");
}
/**
* @return Is the given user a member of this group?
*
* @param user User specified by username.
*
* @param group Group the user might be a member of.
*/
static bool matchUser(std::string_view user, const struct group & gr)
{
for (char * * mem = gr.gr_mem; *mem; mem++)
if (user == std::string_view(*mem)) return true;
return false;
}
/**
* Does the given user (specified by user name and primary group name)
* match the given user/group whitelist?
*
* If the list allows all users: Yes.
*
* If the username is in the set: Yes.
*
* If the groupname is in the set: Yes.
*
* If the user is in another group which is in the set: yes.
*
* Otherwise: No.
*/
static bool matchUser(const std::string & user, const std::string & group, const Strings & users)
{
if (find(users.begin(), users.end(), "*") != users.end())
return true;
if (find(users.begin(), users.end(), user) != users.end())
return true;
for (auto & i : users)
if (i.substr(0, 1) == "@") {
if (group == i.substr(1)) return true;
struct group * gr = getgrnam(i.c_str() + 1);
if (!gr) continue;
if (matchUser(user, *gr)) return true;
}
return false;
}
struct PeerInfo
{
bool pidKnown;
pid_t pid;
bool uidKnown;
uid_t uid;
bool gidKnown;
gid_t gid;
};
/**
* Get the identity of the caller, if possible.
*/
static PeerInfo getPeerInfo(int remote)
{
PeerInfo peer = { false, 0, false, 0, false, 0 };
#if defined(SO_PEERCRED)
ucred cred;
socklen_t credLen = sizeof(cred);
if (getsockopt(remote, SOL_SOCKET, SO_PEERCRED, &cred, &credLen) == -1)
throw SysError("getting peer credentials");
peer = { true, cred.pid, true, cred.uid, true, cred.gid };
#elif defined(LOCAL_PEERCRED)
#if !defined(SOL_LOCAL)
#define SOL_LOCAL 0
#endif
xucred cred;
socklen_t credLen = sizeof(cred);
if (getsockopt(remote, SOL_LOCAL, LOCAL_PEERCRED, &cred, &credLen) == -1)
throw SysError("getting peer credentials");
peer = { false, 0, true, cred.cr_uid, false, 0 };
#endif
return peer;
}
#define SD_LISTEN_FDS_START 3
/**
* Open a store without a path info cache.
*/
static ref<Store> openUncachedStore()
{
Store::Params params; // FIXME: get params from somewhere
// Disable caching since the client already does that.
params["path-info-cache-size"] = "0";
return openStore(settings.storeUri, params);
}
/**
* Authenticate a potential client
*
* @param peer Information about other end of the connection, the client which
* wants to communicate with us.
*
* @return A pair of a `TrustedFlag`, whether the potential client is trusted,
* and the name of the user (useful for printing messages).
*
* If the potential client is not allowed to talk to us, we throw an `Error`.
*/
static std::pair<TrustedFlag, std::string> authPeer(const PeerInfo & peer)
{
TrustedFlag trusted = NotTrusted;
struct passwd * pw = peer.uidKnown ? getpwuid(peer.uid) : 0;
std::string user = pw ? pw->pw_name : std::to_string(peer.uid);
struct group * gr = peer.gidKnown ? getgrgid(peer.gid) : 0;
std::string group = gr ? gr->gr_name : std::to_string(peer.gid);
const Strings & trustedUsers = authorizationSettings.trustedUsers;
const Strings & allowedUsers = authorizationSettings.allowedUsers;
if (matchUser(user, group, trustedUsers))
trusted = Trusted;
if ((!trusted && !matchUser(user, group, allowedUsers)) || group == settings.buildUsersGroup)
throw Error("user '%1%' is not allowed to connect to the Nix daemon", user);
return { trusted, std::move(user) };
}
/**
* Run a server. The loop opens a socket and accepts new connections from that
* socket.
*
* @param forceTrustClientOpt If present, force trusting or not trusted
* the client. Otherwise, decide based on the authentication settings
* and user credentials (from the unix domain socket).
*/
static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
{
if (chdir("/") == -1)
throw SysError("cannot change current directory");
AutoCloseFD fdSocket;
// Handle socket-based activation by systemd.
auto listenFds = getEnv("LISTEN_FDS");
if (listenFds) {
if (getEnv("LISTEN_PID") != std::to_string(getpid()) || listenFds != "1")
throw Error("unexpected systemd environment variables");
fdSocket = SD_LISTEN_FDS_START;
closeOnExec(fdSocket.get());
}
// Otherwise, create and bind to a Unix domain socket.
else {
createDirs(dirOf(settings.nixDaemonSocketFile));
fdSocket = createUnixDomainSocket(settings.nixDaemonSocketFile, 0666);
}
// Get rid of children automatically; don't let them become zombies.
setSigChldAction(true);
// Loop accepting connections.
while (1) {
try {
// Accept a connection.
struct sockaddr_un remoteAddr;
socklen_t remoteAddrLen = sizeof(remoteAddr);
AutoCloseFD remote = accept(fdSocket.get(),
(struct sockaddr *) &remoteAddr, &remoteAddrLen);
checkInterrupt();
if (!remote) {
if (errno == EINTR) continue;
throw SysError("accepting connection");
}
closeOnExec(remote.get());
PeerInfo peer { .pidKnown = false };
TrustedFlag trusted;
std::string user;
if (forceTrustClientOpt)
trusted = *forceTrustClientOpt;
else {
peer = getPeerInfo(remote.get());
auto [_trusted, _user] = authPeer(peer);
trusted = _trusted;
user = _user;
};
printInfo((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""),
peer.pidKnown ? std::to_string(peer.pid) : "<unknown>",
peer.uidKnown ? user : "<unknown>");
// Fork a child to handle the connection.
ProcessOptions options;
options.errorPrefix = "unexpected Nix daemon error: ";
options.dieWithParent = false;
options.runExitHandlers = true;
options.allowVfork = false;
startProcess([&]() {
fdSocket = -1;
// Background the daemon.
if (setsid() == -1)
throw SysError("creating a new session");
// Restore normal handling of SIGCHLD.
setSigChldAction(false);
// For debugging, stuff the pid into argv[1].
if (peer.pidKnown && savedArgv[1]) {
auto processName = std::to_string(peer.pid);
strncpy(savedArgv[1], processName.c_str(), strlen(savedArgv[1]));
}
// Handle the connection.
FdSource from(remote.get());
FdSink to(remote.get());
processConnection(openUncachedStore(), from, to, trusted, NotRecursive);
exit(0);
}, options);
} catch (Interrupted & e) {
return;
} catch (Error & error) {
auto ei = error.info();
// FIXME: add to trace?
ei.msg = hintfmt("error processing connection: %1%", ei.msg.str());
logError(ei);
}
}
}
/**
* Forward a standard IO connection to the given remote store.
*
* We just act as a middleman blindly ferry output between the standard
* input/output and the remote store connection, not processing anything.
*
* Loops until standard input disconnects, or an error is encountered.
*/
static void forwardStdioConnection(RemoteStore & store) {
auto conn = store.openConnectionWrapper();
int from = conn->from.fd;
int to = conn->to.fd;
auto nfds = std::max(from, STDIN_FILENO) + 1;
while (true) {
fd_set fds;
FD_ZERO(&fds);
FD_SET(from, &fds);
FD_SET(STDIN_FILENO, &fds);
if (select(nfds, &fds, nullptr, nullptr, nullptr) == -1)
throw SysError("waiting for data from client or server");
if (FD_ISSET(from, &fds)) {
auto res = splice(from, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
if (res == -1)
throw SysError("splicing data from daemon socket to stdout");
else if (res == 0)
throw EndOfFile("unexpected EOF from daemon socket");
}
if (FD_ISSET(STDIN_FILENO, &fds)) {
auto res = splice(STDIN_FILENO, nullptr, to, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
if (res == -1)
throw SysError("splicing data from stdin to daemon socket");
else if (res == 0)
return;
}
}
}
/**
* Process a client connecting to us via standard input/output
*
* Unlike `forwardStdioConnection()` we do process commands ourselves in
* this case, not delegating to another daemon.
*
* @param trustClient Whether to trust the client. Forwarded directly to
* `processConnection()`.
*/
static void processStdioConnection(ref<Store> store, TrustedFlag trustClient)
{
FdSource from(STDIN_FILENO);
FdSink to(STDOUT_FILENO);
processConnection(store, from, to, trustClient, NotRecursive);
}
/**
* Entry point shared between the new CLI `nix daemon` and old CLI
* `nix-daemon`.
*
* @param forceTrustClientOpt See `daemonLoop()` and the parameter with
* the same name over there for details.
*/
static void runDaemon(bool stdio, std::optional<TrustedFlag> forceTrustClientOpt)
{
if (stdio) {
auto store = openUncachedStore();
// If --force-untrusted is passed, we cannot forward the connection and
// must process it ourselves (before delegating to the next store) to
// force untrusting the client.
if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>(); remoteStore && (!forceTrustClientOpt || *forceTrustClientOpt != NotTrusted))
forwardStdioConnection(*remoteStore);
else
// `Trusted` is passed in the auto (no override case) because we
// cannot see who is on the other side of a plain pipe. Limiting
// access to those is explicitly not `nix-daemon`'s responsibility.
processStdioConnection(store, forceTrustClientOpt.value_or(Trusted));
} else
daemonLoop(forceTrustClientOpt);
}
static int main_nix_daemon(int argc, char * * argv)
{
{
auto stdio = false;
std::optional<TrustedFlag> isTrustedOpt = std::nullopt;
parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
if (*arg == "--daemon")
; // ignored for backwards compatibility
else if (*arg == "--help")
showManPage("nix-daemon");
else if (*arg == "--version")
printVersion("nix-daemon");
else if (*arg == "--stdio")
stdio = true;
else if (*arg == "--force-trusted") {
experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
isTrustedOpt = Trusted;
} else if (*arg == "--force-untrusted") {
experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
isTrustedOpt = NotTrusted;
} else if (*arg == "--default-trust") {
experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
isTrustedOpt = std::nullopt;
} else return false;
return true;
});
runDaemon(stdio, isTrustedOpt);
return 0;
}
}
static RegisterLegacyCommand r_nix_daemon("nix-daemon", main_nix_daemon);
struct CmdDaemon : StoreCommand
{
std::string description() override
{
return "daemon to perform store operations on behalf of non-root clients";
}
Category category() override { return catUtility; }
std::string doc() override
{
return
#include "daemon.md"
;
}
void run(ref<Store> store) override
{
runDaemon(false, std::nullopt);
}
};
static auto rCmdDaemon = registerCommand2<CmdDaemon>({"daemon"});