From 0e8fc118b3d2d3bb6f9b0a918bf8ceb3927774cd Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Wed, 10 Dec 2014 16:35:42 +0100 Subject: [PATCH] Use vfork --- src/libutil/util.cc | 31 +++++++++++++++++++++++-------- src/libutil/util.hh | 12 ++++++++++-- src/nix-daemon/nix-daemon.cc | 7 ++++++- 3 files changed, 39 insertions(+), 11 deletions(-) diff --git a/src/libutil/util.cc b/src/libutil/util.cc index 305e470eb..bdd114c5e 100644 --- a/src/libutil/util.cc +++ b/src/libutil/util.cc @@ -863,31 +863,46 @@ void killUser(uid_t uid) ////////////////////////////////////////////////////////////////////// -pid_t startProcess(std::function fun, - bool dieWithParent, const string & errorPrefix, bool runExitHandlers) +/* Wrapper around vfork to prevent the child process from clobbering + the caller's stack frame in the parent. */ +static pid_t doFork(bool allowVfork, std::function fun) __attribute__((noinline)); +static pid_t doFork(bool allowVfork, std::function fun) { +#ifdef __linux__ + pid_t pid = allowVfork ? vfork() : fork(); +#else pid_t pid = fork(); - if (pid == -1) throw SysError("unable to fork"); +#endif + if (pid != 0) return pid; + fun(); + abort(); +} - if (pid == 0) { + +pid_t startProcess(std::function fun, const ProcessOptions & options) +{ + auto wrapper = [&]() { _writeToStderr = 0; try { #if __linux__ - if (dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1) + if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1) throw SysError("setting death signal"); #endif restoreAffinity(); fun(); } catch (std::exception & e) { try { - std::cerr << errorPrefix << e.what() << "\n"; + std::cerr << options.errorPrefix << e.what() << "\n"; } catch (...) { } } catch (...) { } - if (runExitHandlers) + if (options.runExitHandlers) exit(1); else _exit(1); - } + }; + + pid_t pid = doFork(options.allowVfork, wrapper); + if (pid == -1) throw SysError("unable to fork"); return pid; } diff --git a/src/libutil/util.hh b/src/libutil/util.hh index 628b8a0e1..09eb4d6e2 100644 --- a/src/libutil/util.hh +++ b/src/libutil/util.hh @@ -269,8 +269,16 @@ void killUser(uid_t uid); /* Fork a process that runs the given function, and return the child pid to the caller. */ -pid_t startProcess(std::function fun, bool dieWithParent = true, - const string & errorPrefix = "error: ", bool runExitHandlers = false); +struct ProcessOptions +{ + string errorPrefix; + bool dieWithParent; + bool runExitHandlers; + bool allowVfork; + ProcessOptions() : errorPrefix("error: "), dieWithParent(true), runExitHandlers(false), allowVfork(true) { }; +}; + +pid_t startProcess(std::function fun, const ProcessOptions & options = ProcessOptions()); /* Run a program and return its stdout in a string (i.e., like the diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc index 3864ab935..9a8f469ad 100644 --- a/src/nix-daemon/nix-daemon.cc +++ b/src/nix-daemon/nix-daemon.cc @@ -799,6 +799,11 @@ static void daemonLoop(char * * argv) % (peer.uidKnown ? user : "")); /* 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.close(); @@ -821,7 +826,7 @@ static void daemonLoop(char * * argv) processConnection(trusted); exit(0); - }, false, "unexpected Nix daemon error: ", true); + }, options); } catch (Interrupted & e) { throw;