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Merge pull request #8180 from obsidiansystems/factor-out-daemon-cmd-helpers

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Tidy up and comment daemon CLI
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Robert Hensing 2023-04-08 16:57:49 +02:00 committed by GitHub
parent 4411c7d7e0 8f44edc83e
commit 8f0ec323ea
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1 changed files with 157 additions and 56 deletions
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213
src/nix/daemon.cc
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@ -1,3 +1,5 @@
///@file
#include "command.hh"
#include "shared.hh"
#include "local-store.hh"
@ -34,6 +36,19 @@
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{
@ -54,7 +69,9 @@ struct AuthorizationSettings : Config {
> directories that are otherwise inacessible to them.
)"};
/* ?Who we trust to use the daemon in safe ways */
/**
* Who we trust to use the daemon in safe ways
*/
Setting<Strings> allowedUsers{
this, {"*"}, "allowed-users",
R"(
@ -112,8 +129,36 @@ static void setSigChldAction(bool autoReap)
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;
}
bool matchUser(const std::string & user, const std::string & group, const Strings & users)
/**
* 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;
@ -126,8 +171,7 @@ bool matchUser(const std::string & user, const std::string & group, const String
if (group == i.substr(1)) return true;
struct group * gr = getgrnam(i.c_str() + 1);
if (!gr) continue;
for (char * * mem = gr->gr_mem; *mem; mem++)
if (user == std::string(*mem)) return true;
if (matchUser(user, *gr)) return true;
}
return false;
@ -145,7 +189,9 @@ struct PeerInfo
};
// Get the identity of the caller, if possible.
/**
* Get the identity of the caller, if possible.
*/
static PeerInfo getPeerInfo(int remote)
{
PeerInfo peer = { false, 0, false, 0, false, 0 };
@ -179,6 +225,9 @@ static PeerInfo getPeerInfo(int remote)
#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
@ -187,7 +236,44 @@ static ref<Store> openUncachedStore()
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.
*/
static void daemonLoop()
{
if (chdir("/") == -1)
@ -231,23 +317,9 @@ static void daemonLoop()
closeOnExec(remote.get());
TrustedFlag trusted = NotTrusted;
PeerInfo peer = getPeerInfo(remote.get());
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);
Strings trustedUsers = authorizationSettings.trustedUsers;
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);
auto [_trusted, user] = authPeer(peer);
auto trusted = _trusted;
printInfo((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""),
peer.pidKnown ? std::to_string(peer.pid) : "<unknown>",
@ -294,45 +366,74 @@ static void daemonLoop()
}
}
/**
* 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.
*
* @note `Trusted` is unconditionally passed because in this mode we
* blindly trust the standard streams. Limiting access to those is
* explicitly not `nix-daemon`'s responsibility.
*/
static void processStdioConnection(ref<Store> store)
{
FdSource from(STDIN_FILENO);
FdSink to(STDOUT_FILENO);
processConnection(store, from, to, Trusted, NotRecursive);
}
/**
* Entry point shared between the new CLI `nix daemon` and old CLI
* `nix-daemon`.
*/
static void runDaemon(bool stdio)
{
if (stdio) {
if (auto store = openUncachedStore().dynamic_pointer_cast<RemoteStore>()) {
auto conn = store->openConnectionWrapper();
int from = conn->from.fd;
int to = conn->to.fd;
auto store = openUncachedStore();
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;
}
}
} else {
FdSource from(STDIN_FILENO);
FdSink to(STDOUT_FILENO);
/* Auth hook is empty because in this mode we blindly trust the
standard streams. Limiting access to those is explicitly
not `nix-daemon`'s responsibility. */
processConnection(openUncachedStore(), from, to, Trusted, NotRecursive);
}
if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>())
forwardStdioConnection(*remoteStore);
else
processStdioConnection(store);
} else
daemonLoop();
}