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* Do chroot builds in a private namespace. This means that all the

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bind-mounts we do are only visible to the builder process and its
  children.  So accidentally doing "rm -rf" on the chroot directory
  won't wipe out /nix/store and other bind-mounted directories
  anymore.  Also, the bind-mounts in the private namespace disappear
  automatically when the builder exits.
This commit is contained in:
Eelco Dolstra 2008-12-11 17:00:12 +00:00
parent 07cdfb09fb
commit 7c54f1603f
2 changed files with 46 additions and 134 deletions
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1
configure.ac
View file

@ -90,6 +90,7 @@ AC_LANG_POP(C++)
# Check for chroot support (requires chroot() and bind mounts).
AC_CHECK_FUNCS([chroot])
AC_CHECK_HEADERS([sched.h], [], [], [])
AC_CHECK_HEADERS([sys/param.h], [], [], [])
AC_CHECK_HEADERS([sys/mount.h], [], [],
[#ifdef HAVE_SYS_PARAM_H

175
src/libstore/build.cc
View file

@ -33,8 +33,11 @@
#if HAVE_SYS_MOUNT_H
#include <sys/mount.h>
#endif
#if HAVE_SCHED_H
#include <sched.h>
#endif
#define CHROOT_ENABLED HAVE_CHROOT && HAVE_SYS_MOUNT_H && defined(MS_BIND)
#define CHROOT_ENABLED HAVE_CHROOT && HAVE_SYS_MOUNT_H && defined(MS_BIND) && defined(CLONE_NEWNS)
namespace nix {
@ -603,89 +606,6 @@ void deletePathWrapped(const Path & path)
//////////////////////////////////////////////////////////////////////
/* Helper RAII class for automatically unmounting bind-mounts in
chroots. */
struct BindMount
{
Path source, target;
Paths created;
BindMount()
{
}
BindMount(const Path & source, const Path & target)
{
bind(source, target);
}
~BindMount()
{
try {
unbind();
} catch (...) {
ignoreException();
}
}
void bind(const Path & source, const Path & target)
{
#if CHROOT_ENABLED
debug(format("bind mounting `%1%' to `%2%'") % source % target);
this->source = source;
this->target = target;
created = createDirs(target);
if (mount(source.c_str(), target.c_str(), "", MS_BIND, 0) == -1)
throw SysError(format("bind mount from `%1%' to `%2%' failed") % source % target);
#endif
}
void unbind()
{
#if CHROOT_ENABLED
if (source == "") return;
debug(format("unmount bind-mount `%1%'") % target);
/* Urgh. Unmount sometimes doesn't succeed right away because
the mount point is still busy. It shouldn't be, because
we've killed all the build processes by now (at least when
using a build user; see the check in killUser()). But
maybe this is because those processes are still zombies and
are keeping some kernel structures busy (open files,
current directories, etc.). So retry a few times
(actually, a 1 second sleep is almost certainly enough for
the zombies to be cleaned up). */
unsigned int tries = 0;
while (umount(target.c_str()) == -1) {
if (errno == EBUSY && ++tries < 10) {
printMsg(lvlError, format("unmounting `%1%' failed, retrying after 1 second...") % target);
sleep(1);
}
else
throw SysError(format("unmounting bind-mount `%1%' failed") % target);
}
/* Get rid of the directories for the mount point created in
bind(). */
for (Paths::reverse_iterator i = created.rbegin(); i != created.rend(); ++i) {
debug(format("deleting `%1%'") % *i);
if (remove(i->c_str()) == -1)
throw SysError(format("cannot unlink `%1%'") % *i);
}
source = "";
#endif
}
};
//////////////////////////////////////////////////////////////////////
class DerivationGoal : public Goal
{
private:
@ -729,16 +649,8 @@ private:
/* Whether we're currently doing a chroot build. */
bool useChroot;
/* RAII objects to delete the chroot directory and its /tmp
directory. Don't change the order: autoDelChrootTmp has to be
deleted before autoDelChrootRoot. */
boost::shared_ptr<AutoDelete> autoDelChrootRoot;
boost::shared_ptr<AutoDelete> autoDelChrootTmp;
/* In chroot builds, the list of bind mounts currently active.
The destructor of BindMount will cause the binds to be
unmounted. Keep this *below* autoDelChroot* just to be safe! */
list<boost::shared_ptr<BindMount> > bindMounts;
/* RAII object to delete the chroot directory. */
boost::shared_ptr<AutoDelete> autoDelChroot;
typedef void (DerivationGoal::*GoalState)();
GoalState state;
@ -1183,8 +1095,8 @@ void DerivationGoal::buildDone()
deleteTmpDir(true);
/* In chroot builds, unmount the bind mounts ASAP. */
bindMounts.clear(); /* the destructors will do the rest */
/* Delete the chroot (if we were using one). */
autoDelChroot.reset(); /* this runs the destructor */
/* Compute the FS closure of the outputs and register them as
being valid. */
@ -1737,29 +1649,18 @@ void DerivationGoal::startBuilder()
is somewhat pointless anyway. */
useChroot = queryBoolSetting("build-use-chroot", false);
Path chrootRootDir;
Paths dirsInChroot;
if (fixedOutput) useChroot = false;
if (useChroot) {
#if CHROOT_ENABLED
/* Create a temporary directory in which we set up the chroot
environment using bind-mounts.
!!! Bind mounts are potentially dangerous: if the user
cleans up his system by doing "rm -rf
/nix/var/nix/chroots/*", this will recurse into /nix/store
via the bind mounts (and potentially other parts of the
filesystem, depending on the setting of the
`build-chroot-dirs' option). */
environment using bind-mounts. */
chrootRootDir = createTempDir(nixChrootsDir, "chroot-nix");
/* Clean up the chroot directory automatically, but don't
recurse; that would be very very bad if the unmount of a
bind-mount fails. Instead BindMount::unbind() unmounts and
deletes exactly those directories that it created to
produce the mount point, so that after all the BindMount
destructors have run, chrootRootDir should be empty. */
autoDelChrootRoot = boost::shared_ptr<AutoDelete>(new AutoDelete(chrootRootDir, false));
/* Clean up the chroot directory automatically. */
autoDelChroot = boost::shared_ptr<AutoDelete>(new AutoDelete(chrootRootDir));
printMsg(lvlChatty, format("setting up chroot environment in `%1%'") % chrootRootDir);
@ -1772,12 +1673,6 @@ void DerivationGoal::startBuilder()
if (chmod(chrootTmpDir.c_str(), 01777) == -1)
throw SysError("creating /tmp in the chroot");
/* When deleting this, do recurse (the builder might have left
crap there). As long as nothing important is bind-mounted
under /tmp it's okay (and the bind-mounts are unmounted
before autoDelChrootTmp's destructor runs, anyway). */
autoDelChrootTmp = boost::shared_ptr<AutoDelete>(new AutoDelete(chrootTmpDir));
/* Bind-mount a user-configurable set of directories from the
host file system. The `/dev/pts' directory must be mounted
separately so that newly-created pseudo-terminals show
@ -1787,17 +1682,10 @@ void DerivationGoal::startBuilder()
defaultDirs.push_back("/dev/pts");
defaultDirs.push_back("/proc");
Paths dirsInChroot = querySetting("build-chroot-dirs", defaultDirs);
dirsInChroot = querySetting("build-chroot-dirs", defaultDirs);
dirsInChroot.push_front(nixStore);
dirsInChroot.push_front(tmpDir);
/* Push BindMounts at the front of the list so that they get
unmounted in LIFO order. (!!! Does the C++ standard
guarantee that list elements are destroyed in order?) */
for (Paths::iterator i = dirsInChroot.begin(); i != dirsInChroot.end(); ++i)
bindMounts.push_front(boost::shared_ptr<BindMount>(new BindMount(*i, chrootRootDir + *i)));
#else
throw Error("chroot builds are not supported on this platform");
#endif
@ -1829,14 +1717,37 @@ void DerivationGoal::startBuilder()
try { /* child */
#if CHROOT_ENABLED
/* If building in a chroot, do the chroot right away.
initChild() will do a chdir() to the temporary build
directory to make sure the current directory is in the
chroot. (Actually the order doesn't matter, since due
to the bind mount tmpDir and tmpRootDit/tmpDir are the
same directories.) */
if (useChroot && chroot(chrootRootDir.c_str()) == -1)
if (useChroot) {
/* Create our own mount namespace. This means that
all the bind mounts we do will only show up in this
process and its children, and will disappear
automatically when we're done. */
if (unshare(CLONE_NEWNS) == -1)
throw SysError(format("cannot set up a private mount namespace"));
/* Bind-mount all the directories from the "host"
filesystem that we want in the chroot
environment. */
foreach (Paths::iterator, i, dirsInChroot) {
Path source = *i;
Path target = chrootRootDir + source;
printMsg(lvlError, format("bind mounting `%1%' to `%2%'") % source % target);
createDirs(target);
if (mount(source.c_str(), target.c_str(), "", MS_BIND, 0) == -1)
throw SysError(format("bind mount from `%1%' to `%2%' failed") % source % target);
}
/* Do the chroot(). initChild() will do a chdir() to
the temporary build directory to make sure the
current directory is in the chroot. (Actually the
order doesn't matter, since due to the bind mount
tmpDir and tmpRootDit/tmpDir are the same
directories.) */
if (chroot(chrootRootDir.c_str()) == -1)
throw SysError(format("cannot change root directory to `%1%'") % chrootRootDir);
}
#endif
initChild();