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* Don't provide the whole Nix store in the chroot, but only the

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closure of the inputs.  This really enforces that there can't be any
  undeclared dependencies on paths in the store.  This is done by
  creating a fake Nix store and creating bind-mounts or hard-links in
  the fake store for all paths in the closure.  After the build, the
  build output is moved from the fake store to the real store.  TODO:
  the chroot has to be on the same filesystem as the Nix store for
  this to work, but this isn't enforced yet.  (I.e. it only works
  currently if /tmp is on the same FS as /nix/store.)
This commit is contained in:
Eelco Dolstra 2008-12-11 18:57:10 +00:00
parent 652817046b
commit ac5478eb52
1 changed files with 44 additions and 10 deletions
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54
src/libstore/build.cc
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@ -649,6 +649,8 @@ private:
/* Whether we're currently doing a chroot build. */
bool useChroot;
Path chrootRootDir;
/* RAII object to delete the chroot directory. */
boost::shared_ptr<AutoDelete> autoDelChroot;
@ -804,9 +806,7 @@ void DerivationGoal::haveDerivation()
trace("loading derivation");
if (nrFailed != 0) {
printMsg(lvlError,
format("cannot build missing derivation `%1%'")
% drvPath);
printMsg(lvlError, format("cannot build missing derivation `%1%'") % drvPath);
amDone(ecFailed);
return;
}
@ -1062,6 +1062,12 @@ void DerivationGoal::buildDone()
i != drv.outputs.end(); ++i)
{
Path path = i->second.path;
if (useChroot && pathExists(chrootRootDir + path)) {
if (rename((chrootRootDir + path).c_str(), path.c_str()) == -1)
throw SysError(format("moving build output `%1%' from the chroot to the Nix store") % path);
}
if (!pathExists(path)) continue;
struct stat st;
@ -1449,6 +1455,14 @@ DerivationGoal::PrepareBuildReply DerivationGoal::prepareBuild()
}
void chmod(const Path & path, mode_t mode)
{
if (::chmod(path.c_str(), 01777) == -1)
throw SysError(format("setting permissions on `%1%'") % path);
}
void DerivationGoal::startBuilder()
{
startNest(nest, lvlInfo,
@ -1648,7 +1662,6 @@ void DerivationGoal::startBuilder()
work properly. Purity checking for fixed-output derivations
is somewhat pointless anyway. */
useChroot = queryBoolSetting("build-use-chroot", false);
Path chrootRootDir;
Paths dirsInChroot;
if (fixedOutput) useChroot = false;
@ -1669,9 +1682,7 @@ void DerivationGoal::startBuilder()
instead.) */
Path chrootTmpDir = chrootRootDir + "/tmp";
createDirs(chrootTmpDir);
if (chmod(chrootTmpDir.c_str(), 01777) == -1)
throw SysError("creating /tmp in the chroot");
chmod(chrootTmpDir, 01777);
/* Create a /etc/passwd with entries for the build user and
the nobody account. The latter is kind of a hack to
@ -1695,8 +1706,31 @@ void DerivationGoal::startBuilder()
dirsInChroot = querySetting("build-chroot-dirs", defaultDirs);
dirsInChroot.push_front(nixStore);
dirsInChroot.push_front(tmpDir);
/* Make the closure of the inputs available in the chroot,
rather than the whole Nix store. This prevents any access
to undeclared dependencies. Directories are bind-mounted,
while other inputs are hard-linked (since only directories
can be bind-mounted). !!! As an extra security
precaution, make the fake Nix store only writable by the
build user. */
createDirs(chrootRootDir + nixStore);
chmod(chrootRootDir + nixStore, 01777);
foreach (PathSet::iterator, i, inputPaths) {
struct stat st;
if (lstat(i->c_str(), &st))
throw SysError(format("getting attributes of path `%1%'") % *i);
if (S_ISDIR(st.st_mode))
dirsInChroot.push_back(*i);
else {
Path p = chrootRootDir + *i;
if (link(i->c_str(), p.c_str()) == -1)
throw SysError(format("linking `%1%' to `%2%'") % p % *i);
}
}
#else
throw Error("chroot builds are not supported on this platform");
#endif
@ -1742,7 +1776,7 @@ void DerivationGoal::startBuilder()
foreach (Paths::iterator, i, dirsInChroot) {
Path source = *i;
Path target = chrootRootDir + source;
printMsg(lvlError, format("bind mounting `%1%' to `%2%'") % source % target);
debug(format("bind mounting `%1%' to `%2%'") % source % target);
createDirs(target);
@ -1781,7 +1815,7 @@ void DerivationGoal::startBuilder()
safe. Also note that setuid() when run as root sets
the real, effective and saved UIDs. */
if (buildUser.enabled()) {
debug(format("switching to user `%1%'") % buildUser.getUser());
printMsg(lvlChatty, format("switching to user `%1%'") % buildUser.getUser());
if (amPrivileged()) {