lix/src/libmain/shared.cc
Arthur Gautier fa4abe46e2 preloadNSS: document the preload mechanism
Signed-off-by: Arthur Gautier <baloo@superbaloo.net>
2021-10-16 02:55:25 +00:00

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#include "globals.hh"
#include "shared.hh"
#include "store-api.hh"
#include "util.hh"
#include "loggers.hh"
#include <algorithm>
#include <cctype>
#include <exception>
#include <iostream>
#include <mutex>
#include <cstdlib>
#include <sys/time.h>
#include <sys/stat.h>
#include <unistd.h>
#include <signal.h>
#ifdef __linux__
#include <features.h>
#endif
#ifdef __GLIBC__
#include <gnu/lib-names.h>
#include <nss.h>
#include <dlfcn.h>
#endif
#include <openssl/crypto.h>
#include <sodium.h>
namespace nix {
static bool gcWarning = true;
void printGCWarning()
{
if (!gcWarning) return;
static bool haveWarned = false;
warnOnce(haveWarned,
"you did not specify '--add-root'; "
"the result might be removed by the garbage collector");
}
void printMissing(ref<Store> store, const std::vector<DerivedPath> & paths, Verbosity lvl)
{
uint64_t downloadSize, narSize;
StorePathSet willBuild, willSubstitute, unknown;
store->queryMissing(paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
printMissing(store, willBuild, willSubstitute, unknown, downloadSize, narSize, lvl);
}
void printMissing(ref<Store> store, const StorePathSet & willBuild,
const StorePathSet & willSubstitute, const StorePathSet & unknown,
uint64_t downloadSize, uint64_t narSize, Verbosity lvl)
{
if (!willBuild.empty()) {
if (willBuild.size() == 1)
printMsg(lvl, fmt("this derivation will be built:"));
else
printMsg(lvl, fmt("these %d derivations will be built:", willBuild.size()));
auto sorted = store->topoSortPaths(willBuild);
reverse(sorted.begin(), sorted.end());
for (auto & i : sorted)
printMsg(lvl, fmt(" %s", store->printStorePath(i)));
}
if (!willSubstitute.empty()) {
const float downloadSizeMiB = downloadSize / (1024.f * 1024.f);
const float narSizeMiB = narSize / (1024.f * 1024.f);
if (willSubstitute.size() == 1) {
printMsg(lvl, fmt("this path will be fetched (%.2f MiB download, %.2f MiB unpacked):",
downloadSizeMiB,
narSizeMiB));
} else {
printMsg(lvl, fmt("these %d paths will be fetched (%.2f MiB download, %.2f MiB unpacked):",
willSubstitute.size(),
downloadSizeMiB,
narSizeMiB));
}
for (auto & i : willSubstitute)
printMsg(lvl, fmt(" %s", store->printStorePath(i)));
}
if (!unknown.empty()) {
printMsg(lvl, fmt("don't know how to build these paths%s:",
(settings.readOnlyMode ? " (may be caused by read-only store access)" : "")));
for (auto & i : unknown)
printMsg(lvl, fmt(" %s", store->printStorePath(i)));
}
}
string getArg(const string & opt,
Strings::iterator & i, const Strings::iterator & end)
{
++i;
if (i == end) throw UsageError("'%1%' requires an argument", opt);
return *i;
}
#if OPENSSL_VERSION_NUMBER < 0x10101000L
/* OpenSSL is not thread-safe by default - it will randomly crash
unless the user supplies a mutex locking function. So let's do
that. */
static std::vector<std::mutex> opensslLocks;
static void opensslLockCallback(int mode, int type, const char * file, int line)
{
if (mode & CRYPTO_LOCK)
opensslLocks[type].lock();
else
opensslLocks[type].unlock();
}
#endif
static std::once_flag dns_resolve_flag;
static void preloadNSS() {
/* builtin:fetchurl can trigger a DNS lookup, which with glibc can trigger a dynamic library load of
one of the glibc NSS libraries in a sandboxed child, which will fail unless the library's already
been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to
load its lookup libraries in the parent before any child gets a chance to. */
std::call_once(dns_resolve_flag, []() {
#ifdef __GLIBC__
/* On linux, glibc will run every lookup through the nss layer.
* That means every lookup goes, by default, through nscd, which acts as a local
* cache.
* Because we run builds in a sandbox, we also remove access to nscd otherwise
* lookups would leak into the sandbox.
*
* But now we have a new problem, we need to make sure the nss_dns backend that
* does the dns lookups when nscd is not available is loaded or available.
*
* We can't make it available without leaking nix's environment, so instead we'll
* load the backend, and configure nss so it does not try to run dns lookups
* through nscd.
*
* This is technically only used for builtins:fetch* functions so we only care
* about dns.
*
* All other platforms are unaffected.
*/
if (dlopen (LIBNSS_DNS_SO, RTLD_NOW) == NULL) {
printMsg(Verbosity::lvlWarn, fmt("Unable to load nss_dns backend"));
}
__nss_configure_lookup ("hosts", "dns");
#endif
});
}
static void sigHandler(int signo) { }
void initNix()
{
/* Turn on buffering for cerr. */
#if HAVE_PUBSETBUF
static char buf[1024];
std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
#endif
#if OPENSSL_VERSION_NUMBER < 0x10101000L
/* Initialise OpenSSL locking. */
opensslLocks = std::vector<std::mutex>(CRYPTO_num_locks());
CRYPTO_set_locking_callback(opensslLockCallback);
#endif
if (sodium_init() == -1)
throw Error("could not initialise libsodium");
loadConfFile();
startSignalHandlerThread();
/* Reset SIGCHLD to its default. */
struct sigaction act;
sigemptyset(&act.sa_mask);
act.sa_handler = SIG_DFL;
act.sa_flags = 0;
if (sigaction(SIGCHLD, &act, 0))
throw SysError("resetting SIGCHLD");
/* Install a dummy SIGUSR1 handler for use with pthread_kill(). */
act.sa_handler = sigHandler;
if (sigaction(SIGUSR1, &act, 0)) throw SysError("handling SIGUSR1");
#if __APPLE__
/* HACK: on darwin, we need cant use sigprocmask with SIGWINCH.
* Instead, add a dummy sigaction handler, and signalHandlerThread
* can handle the rest. */
struct sigaction sa;
sa.sa_handler = sigHandler;
if (sigaction(SIGWINCH, &sa, 0)) throw SysError("handling SIGWINCH");
#endif
/* Register a SIGSEGV handler to detect stack overflows. */
detectStackOverflow();
/* There is no privacy in the Nix system ;-) At least not for
now. In particular, store objects should be readable by
everybody. */
umask(0022);
/* Initialise the PRNG. */
struct timeval tv;
gettimeofday(&tv, 0);
srandom(tv.tv_usec);
/* On macOS, don't use the per-session TMPDIR (as set e.g. by
sshd). This breaks build users because they don't have access
to the TMPDIR, in particular in nix-store --serve. */
#if __APPLE__
if (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
unsetenv("TMPDIR");
#endif
preloadNSS();
}
LegacyArgs::LegacyArgs(const std::string & programName,
std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
: MixCommonArgs(programName), parseArg(parseArg)
{
addFlag({
.longName = "no-build-output",
.shortName = 'Q',
.description = "Do not show build output.",
.handler = {[&]() {setLogFormat(LogFormat::raw); }},
});
addFlag({
.longName = "keep-failed",
.shortName ='K',
.description = "Keep temporary directories of failed builds.",
.handler = {&(bool&) settings.keepFailed, true},
});
addFlag({
.longName = "keep-going",
.shortName ='k',
.description = "Keep going after a build fails.",
.handler = {&(bool&) settings.keepGoing, true},
});
addFlag({
.longName = "fallback",
.description = "Build from source if substitution fails.",
.handler = {&(bool&) settings.tryFallback, true},
});
auto intSettingAlias = [&](char shortName, const std::string & longName,
const std::string & description, const std::string & dest)
{
addFlag({
.longName = longName,
.shortName = shortName,
.description = description,
.labels = {"n"},
.handler = {[=](std::string s) {
auto n = string2IntWithUnitPrefix<uint64_t>(s);
settings.set(dest, std::to_string(n));
}}
});
};
intSettingAlias(0, "cores", "Maximum number of CPU cores to use inside a build.", "cores");
intSettingAlias(0, "max-silent-time", "Number of seconds of silence before a build is killed.", "max-silent-time");
intSettingAlias(0, "timeout", "Number of seconds before a build is killed.", "timeout");
addFlag({
.longName = "readonly-mode",
.description = "Do not write to the Nix store.",
.handler = {&settings.readOnlyMode, true},
});
addFlag({
.longName = "no-gc-warning",
.description = "Disable warnings about not using `--add-root`.",
.handler = {&gcWarning, false},
});
addFlag({
.longName = "store",
.description = "The URL of the Nix store to use.",
.labels = {"store-uri"},
.handler = {&(std::string&) settings.storeUri},
});
}
bool LegacyArgs::processFlag(Strings::iterator & pos, Strings::iterator end)
{
if (MixCommonArgs::processFlag(pos, end)) return true;
bool res = parseArg(pos, end);
if (res) ++pos;
return res;
}
bool LegacyArgs::processArgs(const Strings & args, bool finish)
{
if (args.empty()) return true;
assert(args.size() == 1);
Strings ss(args);
auto pos = ss.begin();
if (!parseArg(pos, ss.end()))
throw UsageError("unexpected argument '%1%'", args.front());
return true;
}
void parseCmdLine(int argc, char * * argv,
std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
{
parseCmdLine(std::string(baseNameOf(argv[0])), argvToStrings(argc, argv), parseArg);
}
void parseCmdLine(const string & programName, const Strings & args,
std::function<bool(Strings::iterator & arg, const Strings::iterator & end)> parseArg)
{
LegacyArgs(programName, parseArg).parseCmdline(args);
}
void printVersion(const string & programName)
{
std::cout << format("%1% (Nix) %2%") % programName % nixVersion << std::endl;
if (verbosity > lvlInfo) {
Strings cfg;
#if HAVE_BOEHMGC
cfg.push_back("gc");
#endif
cfg.push_back("signed-caches");
std::cout << "System type: " << settings.thisSystem << "\n";
std::cout << "Additional system types: " << concatStringsSep(", ", settings.extraPlatforms.get()) << "\n";
std::cout << "Features: " << concatStringsSep(", ", cfg) << "\n";
std::cout << "System configuration file: " << settings.nixConfDir + "/nix.conf" << "\n";
std::cout << "User configuration files: " <<
concatStringsSep(":", settings.nixUserConfFiles)
<< "\n";
std::cout << "Store directory: " << settings.nixStore << "\n";
std::cout << "State directory: " << settings.nixStateDir << "\n";
}
throw Exit();
}
void showManPage(const string & name)
{
restoreProcessContext();
setenv("MANPATH", settings.nixManDir.c_str(), 1);
execlp("man", "man", name.c_str(), nullptr);
throw SysError("command 'man %1%' failed", name.c_str());
}
int handleExceptions(const string & programName, std::function<void()> fun)
{
ReceiveInterrupts receiveInterrupts; // FIXME: need better place for this
ErrorInfo::programName = baseNameOf(programName);
string error = ANSI_RED "error:" ANSI_NORMAL " ";
try {
try {
fun();
} catch (...) {
/* Subtle: we have to make sure that any `interrupted'
condition is discharged before we reach printMsg()
below, since otherwise it will throw an (uncaught)
exception. */
setInterruptThrown();
throw;
}
} catch (Exit & e) {
return e.status;
} catch (UsageError & e) {
logError(e.info());
printError("Try '%1% --help' for more information.", programName);
return 1;
} catch (BaseError & e) {
logError(e.info());
if (e.hasTrace() && !loggerSettings.showTrace.get())
printError("(use '--show-trace' to show detailed location information)");
return e.status;
} catch (std::bad_alloc & e) {
printError(error + "out of memory");
return 1;
} catch (std::exception & e) {
printError(error + e.what());
return 1;
}
return 0;
}
RunPager::RunPager()
{
if (!isatty(STDOUT_FILENO)) return;
char * pager = getenv("NIX_PAGER");
if (!pager) pager = getenv("PAGER");
if (pager && ((string) pager == "" || (string) pager == "cat")) return;
Pipe toPager;
toPager.create();
pid = startProcess([&]() {
if (dup2(toPager.readSide.get(), STDIN_FILENO) == -1)
throw SysError("dupping stdin");
if (!getenv("LESS"))
setenv("LESS", "FRSXMK", 1);
restoreProcessContext();
if (pager)
execl("/bin/sh", "sh", "-c", pager, nullptr);
execlp("pager", "pager", nullptr);
execlp("less", "less", nullptr);
execlp("more", "more", nullptr);
throw SysError("executing '%1%'", pager);
});
pid.setKillSignal(SIGINT);
if (dup2(toPager.writeSide.get(), STDOUT_FILENO) == -1)
throw SysError("dupping stdout");
}
RunPager::~RunPager()
{
try {
if (pid != -1) {
std::cout.flush();
close(STDOUT_FILENO);
pid.wait();
}
} catch (...) {
ignoreException();
}
}
PrintFreed::~PrintFreed()
{
if (show)
std::cout << fmt("%d store paths deleted, %s freed\n",
results.paths.size(),
showBytes(results.bytesFreed));
}
Exit::~Exit() { }
}