fix(3p/nix): do not call vfork
The use of vfork() in Nix is entirely illegal. Quote: If the process created by vfork() returns from the function in which vfork() was called, or calls any other function before successfully calling _exit() or one of the exec*() family of functions, the behavior is undefined. -- Linux man-pages, release 5.05 Add a TODO to use the higher-performance variants of clone() on Linux when it is available. Change-Id: I42370e1568ad6e2d00d70d0b66c8aded8f1288bb Reviewed-on: https://cl.tvl.fyi/c/depot/+/1418 Tested-by: BuildkiteCI Reviewed-by: tazjin <mail@tazj.in> Reviewed-by: Alyssa Ross <hi@alyssa.is>
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4 changed files with 12 additions and 21 deletions
3
third_party/nix/src/libstore/build.cc
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3
third_party/nix/src/libstore/build.cc
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@ -2342,8 +2342,6 @@ void DerivationGoal::startBuilder() {
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userNamespaceSync.create();
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options.allowVfork = false;
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Pid helper = startProcess(
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[&]() {
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/* Drop additional groups here because we can't do it
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@ -2443,7 +2441,6 @@ void DerivationGoal::startBuilder() {
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#endif
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{
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fallback:
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options.allowVfork = !buildUser && !drv->isBuiltin();
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pid = startProcess([&]() { runChild(); }, options);
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}
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28
third_party/nix/src/libutil/util.cc
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28
third_party/nix/src/libutil/util.cc
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@ -859,7 +859,6 @@ void killUser(uid_t uid) {
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fork a process, switch to uid, and send a mass kill. */
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ProcessOptions options;
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options.allowVfork = false;
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Pid pid = startProcess(
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[&]() {
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@ -897,16 +896,19 @@ void killUser(uid_t uid) {
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//////////////////////////////////////////////////////////////////////
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/* Wrapper around vfork to prevent the child process from clobbering
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the caller's stack frame in the parent. */
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static pid_t doFork(bool allowVfork, const std::function<void()>& fun)
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__attribute__((noinline));
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static pid_t doFork(bool allowVfork, const std::function<void()>& fun) {
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/*
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* Please note that it is not legal for this function to call vfork(). If the
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* process created by vfork() returns from the function in which vfork() was
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* called, or calls any other function before successfully calling _exit() or
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* one of the exec*() family of functions, the behavior is undefined.
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*/
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static pid_t doFork(const std::function<void()>& fun) __attribute__((noinline));
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static pid_t doFork(const std::function<void()>& fun) {
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#ifdef __linux__
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pid_t pid = allowVfork ? vfork() : fork();
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#else
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pid_t pid = fork();
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// TODO(kanepyork): call clone() instead for faster forking
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#endif
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pid_t pid = fork();
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if (pid != 0) {
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return pid;
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}
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@ -938,7 +940,7 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions& options) {
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}
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};
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pid_t pid = doFork(options.allowVfork, wrapper);
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pid_t pid = doFork(wrapper);
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if (pid == -1) {
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throw SysError("unable to fork");
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}
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@ -1012,12 +1014,6 @@ void runProgram2(const RunOptions& options) {
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}
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ProcessOptions processOptions;
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// vfork implies that the environment of the main process and the fork will
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// be shared (technically this is undefined, but in practice that's the
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// case), so we can't use it if we alter the environment
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if (options.environment) {
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processOptions.allowVfork = false;
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}
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/* Fork. */
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Pid pid = startProcess(
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1
third_party/nix/src/libutil/util.hh
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1
third_party/nix/src/libutil/util.hh
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@ -232,7 +232,6 @@ struct ProcessOptions {
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std::string errorPrefix = "error: ";
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bool dieWithParent = true;
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bool runExitHandlers = false;
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bool allowVfork = true;
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};
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pid_t startProcess(std::function<void()> fun,
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1
third_party/nix/src/nix-daemon/nix-daemon.cc
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third_party/nix/src/nix-daemon/nix-daemon.cc
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@ -1051,7 +1051,6 @@ static void daemonLoop(char** argv) {
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options.errorPrefix = "unexpected Nix daemon error: ";
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options.dieWithParent = false;
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options.runExitHandlers = true;
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options.allowVfork = false;
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startProcess(
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[&]() {
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fdSocket = -1;
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