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* Beginning of secure multi-user Nix stores. If Nix is started as

Browse source 
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 2005-10-17 15:33:24 +00:00
parent 15ff877438
commit 32282abcea
4 changed files with 219 additions and 58 deletions
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5
src/libmain/shared.cc
View file

@ -334,6 +334,11 @@ void switchToNixUser()
exit(1);
}
/* !!! for setuid operation, we should: 1) wipe the environment;
2) verify file descriptors 0, 1, 2; 3) etc.
See: http://www.daemon-systems.org/man/setuid.7.html
*/
haveSwitched = true;
#endif

259
src/libstore/build.cc
View file

@ -1,4 +1,5 @@
#include <map>
#include <sstream>
#include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
@ -9,6 +10,9 @@
#include <unistd.h>
#include <errno.h>
#include <pwd.h>
#include <grp.h>
#include "build.hh"
#include "references.hh"
#include "pathlocks.hh"
@ -22,6 +26,9 @@
static string pathNullDevice = "/dev/null";
static const uid_t rootUserId = 0;
/* Forward definition. */
class Worker;
@ -84,7 +91,12 @@ public:
virtual void waiteeDone(GoalPtr waitee, bool success);
virtual void writeLog(int fd, const unsigned char * buf, size_t count)
virtual void handleChildOutput(int fd, const string & data)
{
abort();
}
virtual void handleEOF(int fd)
{
abort();
}
@ -100,18 +112,19 @@ public:
{
return exitCode;
}
protected:
void amDone(bool success = true);
};
/* A mapping used to remember for each child process to what goal it
belongs, and a file descriptor for receiving log data. */
belongs, and file descriptors for receiving log data and output
path creation commands. */
struct Child
{
WeakGoalPtr goal;
int fdOutput;
set<int> fds;
bool inBuildSlot;
};
@ -166,8 +179,8 @@ public:
bool canBuildMore();
/* Registers / unregisters a running child process. */
void childStarted(GoalPtr goal, pid_t pid, int fdOutput,
bool inBuildSlot);
void childStarted(GoalPtr goal, pid_t pid,
const set<int> & fds, bool inBuildSlot);
void childTerminated(pid_t pid, bool wakeSleepers = true);
/* Add a goal to the set of goals waiting for a build slot. */
@ -299,7 +312,6 @@ const char * * strings2CharPtrs(const Strings & ss)
}
//////////////////////////////////////////////////////////////////////
@ -324,6 +336,9 @@ private:
/* Referenceable paths (i.e., input and output paths). */
PathSet allPaths;
/* User selected for running the builder. */
uid_t buildUser;
/* The process ID of the builder. */
Pid pid;
@ -333,6 +348,13 @@ private:
/* File descriptor for the log file. */
AutoCloseFD fdLogFile;
/* File descriptor for the output creation fifo. */
AutoCloseFD fdCreateOutput;
AutoCloseFD fdOutputCreated;
Path pathCreateOutput;
Path pathOutputCreated;
/* Pipe for the builder's standard output/error. */
Pipe logPipe;
@ -396,7 +418,8 @@ private:
void deleteTmpDir(bool force);
/* Callback used by the worker to write to the log. */
void writeLog(int fd, const unsigned char * buf, size_t count);
void handleChildOutput(int fd, const string & data);
void handleEOF(int fd);
/* Return the set of (in)valid paths. */
PathSet checkPathValidity(bool returnValid);
@ -408,6 +431,7 @@ DerivationGoal::DerivationGoal(const Path & drvPath, Worker & worker)
{
this->drvPath = drvPath;
state = &DerivationGoal::init;
buildUser = 0;
name = (format("building of `%1%'") % drvPath).str();
trace("created");
}
@ -607,7 +631,8 @@ void DerivationGoal::buildDone()
to have terminated. In fact, the builder could also have
simply have closed its end of the pipe --- just don't do that
:-) */
/* !!! this could block! */
/* !!! this could block! security problem! solution: kill the
child */
pid_t savedPid = pid;
int status = pid.wait(true);
@ -757,7 +782,7 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
/* parent */
logPipe.writeSide.close();
worker.childStarted(shared_from_this(),
pid, logPipe.readSide, false);
pid, singleton<set<int> >(logPipe.readSide), false);
fromHook.writeSide.close();
toHook.readSide.close();
@ -953,6 +978,29 @@ bool DerivationGoal::prepareBuild()
}
static uid_t allocBuildUser()
{
Strings buildUsers = querySetting("build-users", Strings());
if (buildUsers.empty())
throw Error(
"cannot build as `root'; you must define "
"one or more users for building in `build-users' "
"in the Nix configuration file");
for (Strings::iterator i = buildUsers.begin(); i != buildUsers.end(); ++i) {
printMsg(lvlError, format("trying user `%1%'") % *i);
struct passwd * pw = getpwnam(i->c_str());
if (!pw)
throw Error(format("the user `%1%' listed in `build-users' does not exist") % *i);
return pw->pw_uid;
}
}
void DerivationGoal::startBuilder()
{
startNest(nest, lvlInfo,
@ -1026,6 +1074,39 @@ void DerivationGoal::startBuilder()
if (i->second.hash != "")
env["NIX_OUTPUT_CHECKED"] = "1";
/* Create the FIFOs through which the child can tell this process
to create the output path. */
pathCreateOutput = tmpDir + "/.create-output.fifo";
pathOutputCreated = tmpDir + "/.output-created.fifo";
if (mkfifo(pathCreateOutput.c_str(), 0622) == -1 ||
chmod(pathCreateOutput.c_str(), 0622) == -1)
throw SysError(format("cannot create FIFO `%1%'") % pathCreateOutput);
if (mkfifo(pathOutputCreated.c_str(), 0700) == -1 ||
chmod(pathOutputCreated.c_str(), 0622) == -1)
throw SysError(format("cannot create FIFO `%1%'") % pathOutputCreated);
fdCreateOutput = open(pathCreateOutput.c_str(), O_RDONLY | O_NONBLOCK);
if (fdCreateOutput == -1)
throw SysError(format("cannot open FIFO `%1%'") % pathCreateOutput);
/* If we are running as root, and the `build-allow-root' setting
is `false', then we have to build as one of the users listed in
`build-users'. */
if (!queryBoolSetting("build-allow-root", true) &&
getuid() == rootUserId)
{
buildUser = allocBuildUser();
/* Change ownership of the temporary build directory. !!! gid */
if (chown(tmpDir.c_str(), buildUser, (gid_t) -1) == -1)
throw SysError(format("cannot change ownership of `%1%'") % tmpDir);
}
/* Run the builder. */
printMsg(lvlChatty, format("executing builder `%1%'") %
drv.builder);
@ -1064,6 +1145,25 @@ void DerivationGoal::startBuilder()
envStrs.push_back(i->first + "=" + i->second);
const char * * envArr = strings2CharPtrs(envStrs);
/* If we are running as root and `build-allow-root' is
`false', then switch to the user we allocated above.
Make sure that we drop all root privileges. Note that
initChild() above has closed all file descriptors
except std*, so that's safe. Also note that setuid()
when run as root sets the real, effective and saved
UIDs. */
if (buildUser != 0) {
printMsg(lvlError, format("switching to uid `%1%'") % buildUser);
/* !!! setgid also */
if (setgroups(0, 0) == -1)
throw SysError("cannot clear the set of supplementary groups");
setuid(buildUser);
assert(getuid() == buildUser);
assert(geteuid() == buildUser);
}
/* Execute the program. This should not return. */
execve(drv.builder.c_str(),
(char * *) argArr, (char * *) envArr);
@ -1077,11 +1177,14 @@ void DerivationGoal::startBuilder()
_exit(1);
}
/* parent */
pid.setSeparatePG(true);
logPipe.writeSide.close();
worker.childStarted(shared_from_this(),
pid, logPipe.readSide, true);
set<int> fds;
fds.insert(logPipe.readSide);
fds.insert(fdCreateOutput);
worker.childStarted(shared_from_this(), pid, fds, true);
}
@ -1270,11 +1373,60 @@ void DerivationGoal::deleteTmpDir(bool force)
}
void DerivationGoal::writeLog(int fd,
const unsigned char * buf, size_t count)
void DerivationGoal::handleChildOutput(int fd, const string & data)
{
assert(fd == logPipe.readSide);
writeFull(fdLogFile, buf, count);
if (fd == logPipe.readSide) {
if (verbosity >= buildVerbosity)
writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
writeFull(fdLogFile, (unsigned char *) data.c_str(), data.size());
}
else if (fd == fdCreateOutput) {
/* The child sent us a command to create the output path. */
debug(format("got output creation command `%1%'") % data);
istringstream str(data);
string id, type;
str >> id >> type;
if (id != "out") throw Error("not supported!"); /* !!! */
Path path;
for (DerivationOutputs::const_iterator i = drv.outputs.begin();
i != drv.outputs.end(); ++i)
if (i->first == "out") path = i->second.path.c_str();
if (path.empty()) throw Error(format("unknown output ID `%1%'") % id);
if (type == "d") {
if (mkdir(path.c_str(), 0700) == -1)
throw SysError(format("creating directory `%1%'") % path);
} else if (type == "f") {
AutoCloseFD fd = open(path.c_str(), O_CREAT | O_EXCL | O_RDONLY, 0600);
if (fd == -1)
throw SysError(format("creating file `%1%'") % path);
} else
throw Error(format("bad output creation command `%1%'") % type);
if (chown(path.c_str(), buildUser, (gid_t) -1) == -1) /* !!! */
throw SysError(format("cannot change ownership of `%1%'") % path);
/* The builder must open this FIFO for writing. This will
block until we have opened it for reading. Here we do
so, causing the builder to unblock and proceed. */
fdOutputCreated = open(pathOutputCreated.c_str(), O_RDONLY | O_NONBLOCK);
if (fdOutputCreated == -1)
throw SysError(format("cannot open FIFO `%1%'") % pathOutputCreated);
}
else abort();
}
void DerivationGoal::handleEOF(int fd)
{
if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
}
@ -1337,7 +1489,8 @@ public:
void finished();
/* Callback used by the worker to write to the log. */
void writeLog(int fd, const unsigned char * buf, size_t count);
void handleChildOutput(int fd, const string & data);
void handleEOF(int fd);
};
@ -1502,7 +1655,7 @@ void SubstitutionGoal::tryToRun()
pid.setSeparatePG(true);
logPipe.writeSide.close();
worker.childStarted(shared_from_this(),
pid, logPipe.readSide, true);
pid, singleton<set<int> >(logPipe.readSide), true);
state = &SubstitutionGoal::finished;
}
@ -1569,15 +1722,22 @@ void SubstitutionGoal::finished()
}
void SubstitutionGoal::writeLog(int fd,
const unsigned char * buf, size_t count)
void SubstitutionGoal::handleChildOutput(int fd, const string & data)
{
assert(fd == logPipe.readSide);
if (verbosity >= buildVerbosity)
writeFull(STDERR_FILENO, (unsigned char *) data.c_str(), data.size());
/* Don't write substitution output to a log file for now. We
probably should, though. */
}
void SubstitutionGoal::handleEOF(int fd)
{
if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
}
//////////////////////////////////////////////////////////////////////
@ -1674,11 +1834,11 @@ bool Worker::canBuildMore()
void Worker::childStarted(GoalPtr goal,
pid_t pid, int fdOutput, bool inBuildSlot)
pid_t pid, const set<int> & fds, bool inBuildSlot)
{
Child child;
child.goal = goal;
child.fdOutput = fdOutput;
child.fds = fds;
child.inBuildSlot = inBuildSlot;
children[pid] = child;
if (inBuildSlot) nrChildren++;
@ -1772,9 +1932,11 @@ void Worker::waitForInput()
{
printMsg(lvlVomit, "waiting for children");
/* Process log output from the children. We also use this to
detect child termination: if we get EOF on the logger pipe of a
build, we assume that the builder has terminated. */
/* Process output from the file descriptors attached to the
children, namely log output and output path creation commands.
We also use this to detect child termination: if we get EOF on
the logger pipe of a build, we assume that the builder has
terminated. */
/* Use select() to wait for the input side of any logger pipe to
become `available'. Note that `available' (i.e., non-blocking)
@ -1785,9 +1947,12 @@ void Worker::waitForInput()
for (Children::iterator i = children.begin();
i != children.end(); ++i)
{
int fd = i->second.fdOutput;
FD_SET(fd, &fds);
if (fd >= fdMax) fdMax = fd + 1;
for (set<int>::iterator j = i->second.fds.begin();
j != i->second.fds.end(); ++j)
{
FD_SET(*j, &fds);
if (*j >= fdMax) fdMax = *j + 1;
}
}
if (select(fdMax, &fds, 0, 0, 0) == -1) {
@ -1802,29 +1967,33 @@ void Worker::waitForInput()
checkInterrupt();
GoalPtr goal = i->second.goal.lock();
assert(goal);
int fd = i->second.fdOutput;
if (FD_ISSET(fd, &fds)) {
unsigned char buffer[4096];
ssize_t rd = read(fd, buffer, sizeof(buffer));
if (rd == -1) {
if (errno != EINTR)
throw SysError(format("reading from %1%")
% goal->getName());
} else if (rd == 0) {
debug(format("%1%: got EOF") % goal->getName());
wakeUp(goal);
} else {
printMsg(lvlVomit, format("%1%: read %2% bytes")
% goal->getName() % rd);
goal->writeLog(fd, buffer, (size_t) rd);
if (verbosity >= buildVerbosity)
writeFull(STDERR_FILENO, buffer, rd);
set<int> fds2(i->second.fds);
for (set<int>::iterator j = fds2.begin(); j != fds2.end(); ++j)
{
if (FD_ISSET(*j, &fds)) {
unsigned char buffer[4096];
ssize_t rd = read(*j, buffer, sizeof(buffer));
if (rd == -1) {
if (errno != EINTR)
throw SysError(format("reading from %1%")
% goal->getName());
} else if (rd == 0) {
debug(format("%1%: got EOF") % goal->getName());
goal->handleEOF(*j);
i->second.fds.erase(*j);
} else {
printMsg(lvlVomit, format("%1%: read %2% bytes")
% goal->getName() % rd);
string data((char *) buffer, rd);
goal->handleChildOutput(*j, data);
}
}
}
}
}
//////////////////////////////////////////////////////////////////////

4
src/libstore/globals.cc
View file

@ -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");

9
src/libstore/globals.hh
View file

@ -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);