* Beginning of secure multi-user Nix stores. If Nix is started as
root (or setuid root), then builds will be performed under one of the users listed in the `build-users' configuration variables. This is to make it impossible to influence build results externally, allowing locally built derivations to be shared safely between users (see ASE-2005 paper). To do: only one builder should be active per build user.
This commit is contained in:
Eelco Dolstra
parent
15ff877438
commit
32282abcea
4 changed files with 219 additions and 58 deletions
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@ -334,6 +334,11 @@ void switchToNixUser()
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exit(1);
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}
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/* !!! for setuid operation, we should: 1) wipe the environment;
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2) verify file descriptors 0, 1, 2; 3) etc.
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See: http://www.daemon-systems.org/man/setuid.7.html
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*/
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haveSwitched = true;
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#endif
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@ -1,4 +1,5 @@
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#include <map>
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#include <sstream>
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#include <boost/shared_ptr.hpp>
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#include <boost/weak_ptr.hpp>
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#include <boost/enable_shared_from_this.hpp>
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@ -9,6 +10,9 @@
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#include <unistd.h>
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#include <errno.h>
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#include <pwd.h>
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#include <grp.h>
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#include "build.hh"
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#include "references.hh"
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#include "pathlocks.hh"
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@ -22,6 +26,9 @@
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static string pathNullDevice = "/dev/null";
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static const uid_t rootUserId = 0;
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/* Forward definition. */
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class Worker;
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@ -84,7 +91,12 @@ public:
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virtual void waiteeDone(GoalPtr waitee, bool success);
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virtual void writeLog(int fd, const unsigned char * buf, size_t count)
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virtual void handleChildOutput(int fd, const string & data)
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{
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abort();
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}
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virtual void handleEOF(int fd)
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{
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abort();
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}
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@ -107,11 +119,12 @@ protected:
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/* A mapping used to remember for each child process to what goal it
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belongs, and a file descriptor for receiving log data. */
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belongs, and file descriptors for receiving log data and output
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path creation commands. */
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struct Child
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{
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WeakGoalPtr goal;
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int fdOutput;
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set<int> fds;
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bool inBuildSlot;
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};
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@ -166,8 +179,8 @@ public:
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bool canBuildMore();
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/* Registers / unregisters a running child process. */
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void childStarted(GoalPtr goal, pid_t pid, int fdOutput,
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bool inBuildSlot);
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void childStarted(GoalPtr goal, pid_t pid,
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const set<int> & fds, bool inBuildSlot);
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void childTerminated(pid_t pid, bool wakeSleepers = true);
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/* Add a goal to the set of goals waiting for a build slot. */
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@ -299,7 +312,6 @@ const char * * strings2CharPtrs(const Strings & ss)
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}
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//////////////////////////////////////////////////////////////////////
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@ -324,6 +336,9 @@ private:
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/* Referenceable paths (i.e., input and output paths). */
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PathSet allPaths;
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/* User selected for running the builder. */
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uid_t buildUser;
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/* The process ID of the builder. */
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Pid pid;
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@ -333,6 +348,13 @@ private:
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/* File descriptor for the log file. */
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AutoCloseFD fdLogFile;
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/* File descriptor for the output creation fifo. */
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AutoCloseFD fdCreateOutput;
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AutoCloseFD fdOutputCreated;
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Path pathCreateOutput;
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Path pathOutputCreated;
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/* Pipe for the builder's standard output/error. */
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Pipe logPipe;
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@ -396,7 +418,8 @@ private:
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void deleteTmpDir(bool force);
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/* Callback used by the worker to write to the log. */
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void writeLog(int fd, const unsigned char * buf, size_t count);
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void handleChildOutput(int fd, const string & data);
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void handleEOF(int fd);
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/* Return the set of (in)valid paths. */
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PathSet checkPathValidity(bool returnValid);
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@ -408,6 +431,7 @@ DerivationGoal::DerivationGoal(const Path & drvPath, Worker & worker)
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{
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this->drvPath = drvPath;
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state = &DerivationGoal::init;
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buildUser = 0;
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name = (format("building of `%1%'") % drvPath).str();
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trace("created");
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}
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@ -607,7 +631,8 @@ void DerivationGoal::buildDone()
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to have terminated. In fact, the builder could also have
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simply have closed its end of the pipe --- just don't do that
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:-) */
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/* !!! this could block! */
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/* !!! this could block! security problem! solution: kill the
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child */
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pid_t savedPid = pid;
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int status = pid.wait(true);
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@ -757,7 +782,7 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
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/* parent */
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logPipe.writeSide.close();
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worker.childStarted(shared_from_this(),
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pid, logPipe.readSide, false);
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pid, singleton<set<int> >(logPipe.readSide), false);
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fromHook.writeSide.close();
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toHook.readSide.close();
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@ -953,6 +978,29 @@ bool DerivationGoal::prepareBuild()
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}
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static uid_t allocBuildUser()
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{
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Strings buildUsers = querySetting("build-users", Strings());
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if (buildUsers.empty())
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throw Error(
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"cannot build as `root'; you must define "
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"one or more users for building in `build-users' "
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"in the Nix configuration file");
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for (Strings::iterator i = buildUsers.begin(); i != buildUsers.end(); ++i) {
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printMsg(lvlError, format("trying user `%1%'") % *i);
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struct passwd * pw = getpwnam(i->c_str());
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if (!pw)
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throw Error(format("the user `%1%' listed in `build-users' does not exist") % *i);
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return pw->pw_uid;
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}
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}
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void DerivationGoal::startBuilder()
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{
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startNest(nest, lvlInfo,
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@ -1026,6 +1074,39 @@ void DerivationGoal::startBuilder()
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if (i->second.hash != "")
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env["NIX_OUTPUT_CHECKED"] = "1";
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/* Create the FIFOs through which the child can tell this process
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to create the output path. */
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pathCreateOutput = tmpDir + "/.create-output.fifo";
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pathOutputCreated = tmpDir + "/.output-created.fifo";
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if (mkfifo(pathCreateOutput.c_str(), 0622) == -1 ||
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chmod(pathCreateOutput.c_str(), 0622) == -1)
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throw SysError(format("cannot create FIFO `%1%'") % pathCreateOutput);
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if (mkfifo(pathOutputCreated.c_str(), 0700) == -1 ||
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chmod(pathOutputCreated.c_str(), 0622) == -1)
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throw SysError(format("cannot create FIFO `%1%'") % pathOutputCreated);
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fdCreateOutput = open(pathCreateOutput.c_str(), O_RDONLY | O_NONBLOCK);
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if (fdCreateOutput == -1)
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throw SysError(format("cannot open FIFO `%1%'") % pathCreateOutput);
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/* If we are running as root, and the `build-allow-root' setting
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is `false', then we have to build as one of the users listed in
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`build-users'. */
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if (!queryBoolSetting("build-allow-root", true) &&
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getuid() == rootUserId)
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{
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buildUser = allocBuildUser();
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/* Change ownership of the temporary build directory. !!! gid */
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if (chown(tmpDir.c_str(), buildUser, (gid_t) -1) == -1)
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throw SysError(format("cannot change ownership of `%1%'") % tmpDir);
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}
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/* Run the builder. */
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printMsg(lvlChatty, format("executing builder `%1%'") %
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drv.builder);
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@ -1064,6 +1145,25 @@ void DerivationGoal::startBuilder()
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envStrs.push_back(i->first + "=" + i->second);
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const char * * envArr = strings2CharPtrs(envStrs);
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/* If we are running as root and `build-allow-root' is
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`false', then switch to the user we allocated above.
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Make sure that we drop all root privileges. Note that
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initChild() above has closed all file descriptors
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except std*, so that's safe. Also note that setuid()
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when run as root sets the real, effective and saved
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UIDs. */
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if (buildUser != 0) {
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printMsg(lvlError, format("switching to uid `%1%'") % buildUser);
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/* !!! setgid also */
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if (setgroups(0, 0) == -1)
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throw SysError("cannot clear the set of supplementary groups");
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setuid(buildUser);
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assert(getuid() == buildUser);
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assert(geteuid() == buildUser);
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}
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/* Execute the program. This should not return. */
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execve(drv.builder.c_str(),
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(char * *) argArr, (char * *) envArr);
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@ -1077,11 +1177,14 @@ void DerivationGoal::startBuilder()
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_exit(1);
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}
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/* parent */
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pid.setSeparatePG(true);
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logPipe.writeSide.close();
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worker.childStarted(shared_from_this(),
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pid, logPipe.readSide, true);
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set<int> fds;
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fds.insert(logPipe.readSide);
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fds.insert(fdCreateOutput);
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worker.childStarted(shared_from_this(), pid, fds, true);
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}
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@ -1270,11 +1373,60 @@ void DerivationGoal::deleteTmpDir(bool force)
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}
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void DerivationGoal::writeLog(int fd,
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const unsigned char * buf, size_t count)
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void DerivationGoal::handleChildOutput(int fd, const string & data)
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{
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assert(fd == logPipe.readSide);
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writeFull(fdLogFile, buf, count);
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if (fd == logPipe.readSide) {
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if (verbosity >= buildVerbosity)
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writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
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writeFull(fdLogFile, (unsigned char *) data.c_str(), data.size());
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}
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else if (fd == fdCreateOutput) {
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/* The child sent us a command to create the output path. */
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debug(format("got output creation command `%1%'") % data);
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istringstream str(data);
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string id, type;
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str >> id >> type;
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if (id != "out") throw Error("not supported!"); /* !!! */
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Path path;
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for (DerivationOutputs::const_iterator i = drv.outputs.begin();
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i != drv.outputs.end(); ++i)
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if (i->first == "out") path = i->second.path.c_str();
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if (path.empty()) throw Error(format("unknown output ID `%1%'") % id);
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if (type == "d") {
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if (mkdir(path.c_str(), 0700) == -1)
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throw SysError(format("creating directory `%1%'") % path);
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} else if (type == "f") {
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AutoCloseFD fd = open(path.c_str(), O_CREAT | O_EXCL | O_RDONLY, 0600);
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if (fd == -1)
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throw SysError(format("creating file `%1%'") % path);
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} else
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throw Error(format("bad output creation command `%1%'") % type);
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if (chown(path.c_str(), buildUser, (gid_t) -1) == -1) /* !!! */
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throw SysError(format("cannot change ownership of `%1%'") % path);
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/* The builder must open this FIFO for writing. This will
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block until we have opened it for reading. Here we do
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so, causing the builder to unblock and proceed. */
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fdOutputCreated = open(pathOutputCreated.c_str(), O_RDONLY | O_NONBLOCK);
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if (fdOutputCreated == -1)
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throw SysError(format("cannot open FIFO `%1%'") % pathOutputCreated);
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}
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else abort();
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}
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void DerivationGoal::handleEOF(int fd)
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{
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if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
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}
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@ -1337,7 +1489,8 @@ public:
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void finished();
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/* Callback used by the worker to write to the log. */
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void writeLog(int fd, const unsigned char * buf, size_t count);
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void handleChildOutput(int fd, const string & data);
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void handleEOF(int fd);
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};
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@ -1502,7 +1655,7 @@ void SubstitutionGoal::tryToRun()
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pid.setSeparatePG(true);
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logPipe.writeSide.close();
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worker.childStarted(shared_from_this(),
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pid, logPipe.readSide, true);
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pid, singleton<set<int> >(logPipe.readSide), true);
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state = &SubstitutionGoal::finished;
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}
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@ -1569,15 +1722,22 @@ void SubstitutionGoal::finished()
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}
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void SubstitutionGoal::writeLog(int fd,
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const unsigned char * buf, size_t count)
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void SubstitutionGoal::handleChildOutput(int fd, const string & data)
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{
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assert(fd == logPipe.readSide);
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if (verbosity >= buildVerbosity)
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writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
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/* Don't write substitution output to a log file for now. We
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probably should, though. */
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}
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void SubstitutionGoal::handleEOF(int fd)
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{
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if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
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}
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//////////////////////////////////////////////////////////////////////
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@ -1674,11 +1834,11 @@ bool Worker::canBuildMore()
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void Worker::childStarted(GoalPtr goal,
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pid_t pid, int fdOutput, bool inBuildSlot)
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pid_t pid, const set<int> & fds, bool inBuildSlot)
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{
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Child child;
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child.goal = goal;
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child.fdOutput = fdOutput;
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child.fds = fds;
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child.inBuildSlot = inBuildSlot;
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children[pid] = child;
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if (inBuildSlot) nrChildren++;
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@ -1772,9 +1932,11 @@ void Worker::waitForInput()
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{
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printMsg(lvlVomit, "waiting for children");
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/* Process log output from the children. We also use this to
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detect child termination: if we get EOF on the logger pipe of a
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build, we assume that the builder has terminated. */
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/* Process output from the file descriptors attached to the
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children, namely log output and output path creation commands.
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We also use this to detect child termination: if we get EOF on
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the logger pipe of a build, we assume that the builder has
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terminated. */
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/* Use select() to wait for the input side of any logger pipe to
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become `available'. Note that `available' (i.e., non-blocking)
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@ -1785,9 +1947,12 @@ void Worker::waitForInput()
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for (Children::iterator i = children.begin();
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i != children.end(); ++i)
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{
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int fd = i->second.fdOutput;
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FD_SET(fd, &fds);
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if (fd >= fdMax) fdMax = fd + 1;
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for (set<int>::iterator j = i->second.fds.begin();
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j != i->second.fds.end(); ++j)
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{
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FD_SET(*j, &fds);
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if (*j >= fdMax) fdMax = *j + 1;
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}
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}
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if (select(fdMax, &fds, 0, 0, 0) == -1) {
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@ -1802,29 +1967,33 @@ void Worker::waitForInput()
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checkInterrupt();
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GoalPtr goal = i->second.goal.lock();
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assert(goal);
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int fd = i->second.fdOutput;
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if (FD_ISSET(fd, &fds)) {
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unsigned char buffer[4096];
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ssize_t rd = read(fd, buffer, sizeof(buffer));
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if (rd == -1) {
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if (errno != EINTR)
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throw SysError(format("reading from %1%")
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% goal->getName());
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} else if (rd == 0) {
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debug(format("%1%: got EOF") % goal->getName());
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wakeUp(goal);
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} else {
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printMsg(lvlVomit, format("%1%: read %2% bytes")
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% goal->getName() % rd);
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goal->writeLog(fd, buffer, (size_t) rd);
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if (verbosity >= buildVerbosity)
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writeFull(STDERR_FILENO, buffer, rd);
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set<int> fds2(i->second.fds);
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for (set<int>::iterator j = fds2.begin(); j != fds2.end(); ++j)
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{
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if (FD_ISSET(*j, &fds)) {
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unsigned char buffer[4096];
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ssize_t rd = read(*j, buffer, sizeof(buffer));
|
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if (rd == -1) {
|
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if (errno != EINTR)
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throw SysError(format("reading from %1%")
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% goal->getName());
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} else if (rd == 0) {
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debug(format("%1%: got EOF") % goal->getName());
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goal->handleEOF(*j);
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i->second.fds.erase(*j);
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} else {
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printMsg(lvlVomit, format("%1%: read %2% bytes")
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% goal->getName() % rd);
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string data((char *) buffer, rd);
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goal->handleChildOutput(*j, data);
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}
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}
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}
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}
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}
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//////////////////////////////////////////////////////////////////////
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||||
|
||||
|
||||
|
|
|
|||
|
|
@ -17,8 +17,6 @@ bool tryFallback = false;
|
|||
Verbosity buildVerbosity = lvlInfo;
|
||||
unsigned int maxBuildJobs = 1;
|
||||
bool readOnlyMode = false;
|
||||
bool buildAllowRoot = true;
|
||||
list<string> buildUsers;
|
||||
|
||||
|
||||
static bool settingsRead = false;
|
||||
|
|
@ -79,8 +77,6 @@ Strings querySetting(const string & name, const Strings & def)
|
|||
|
||||
bool queryBoolSetting(const string & name, bool def)
|
||||
{
|
||||
debug("X");
|
||||
|
||||
Strings defs;
|
||||
if (def) defs.push_back("true"); else defs.push_back("false");
|
||||
|
||||
|
|
|
|||
|
|
@ -53,15 +53,6 @@ extern unsigned int maxBuildJobs;
|
|||
database. */
|
||||
extern bool readOnlyMode;
|
||||
|
||||
/* Whether to allow builds by root. Corresponds to the
|
||||
`build-allow-root' configuration option. */
|
||||
extern bool buildAllowRoot;
|
||||
|
||||
/* The list of users under which root-initiated builds can be
|
||||
performed. Correspons to the `build-users' configuration
|
||||
option. */
|
||||
extern list<string> buildUsers;
|
||||
|
||||
|
||||
Strings querySetting(const string & name, const Strings & def);
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue