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libstore: Add LocalDerivationGoal prepareSandbox hook

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Add a new OS-specific hook called `prepareSandbox`, run before forking
On Darwin this is empty as nothing is required,
on Linux this creates the chroot directory and adds basic files,
and on platforms using a fallback this throws an exception

Change-Id: Ie30c38c387f2e0e5844b2afa32fd4d33b1180dae
This commit is contained in:
Artemis Tosini 2024-05-19 22:25:30 +00:00 committed by Artemis Tosini
parent 5eec6418de
commit af1dcc2d5e
Signed by untrusted user: artemist
GPG key ID: EE5227935FE3FF18
5 changed files with 131 additions and 94 deletions
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98
src/libstore/build/local-derivation-goal.cc
View file

@ -659,101 +659,11 @@ void LocalDerivationGoal::startBuilder()
pathsInChroot[i] = {i, true};
}
#if __linux__
/* Create a temporary directory in which we set up the chroot
environment using bind-mounts. We put it in the Nix store
to ensure that we can create hard-links to non-directory
inputs in the fake Nix store in the chroot (see below). */
chrootRootDir = worker.store.Store::toRealPath(drvPath) + ".chroot";
deletePath(chrootRootDir);
/* Clean up the chroot directory automatically. */
autoDelChroot = std::make_shared<AutoDelete>(chrootRootDir);
printMsg(lvlChatty, "setting up chroot environment in '%1%'", chrootRootDir);
// FIXME: make this 0700
if (mkdir(chrootRootDir.c_str(), buildUser && buildUser->getUIDCount() != 1 ? 0755 : 0750) == -1)
throw SysError("cannot create '%1%'", chrootRootDir);
if (buildUser && chown(chrootRootDir.c_str(), buildUser->getUIDCount() != 1 ? buildUser->getUID() : 0, buildUser->getGID()) == -1)
throw SysError("cannot change ownership of '%1%'", chrootRootDir);
/* Create a writable /tmp in the chroot. Many builders need
this. (Of course they should really respect $TMPDIR
instead.) */
Path chrootTmpDir = chrootRootDir + "/tmp";
createDirs(chrootTmpDir);
chmodPath(chrootTmpDir, 01777);
/* Create a /etc/passwd with entries for the build user and the
nobody account. The latter is kind of a hack to support
Samba-in-QEMU. */
createDirs(chrootRootDir + "/etc");
if (parsedDrv->useUidRange())
chownToBuilder(chrootRootDir + "/etc");
if (parsedDrv->useUidRange() && (!buildUser || buildUser->getUIDCount() < 65536))
throw Error("feature 'uid-range' requires the setting '%s' to be enabled", settings.autoAllocateUids.name);
/* Create /etc/hosts with localhost entry. */
if (derivationType->isSandboxed())
writeFile(chrootRootDir + "/etc/hosts", "127.0.0.1 localhost\n::1 localhost\n");
/* 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. */
Path chrootStoreDir = chrootRootDir + worker.store.storeDir;
createDirs(chrootStoreDir);
chmodPath(chrootStoreDir, 01775);
if (buildUser && chown(chrootStoreDir.c_str(), 0, buildUser->getGID()) == -1)
throw SysError("cannot change ownership of '%1%'", chrootStoreDir);
for (auto & i : inputPaths) {
auto p = worker.store.printStorePath(i);
Path r = worker.store.toRealPath(p);
pathsInChroot.insert_or_assign(p, r);
}
/* If we're repairing, checking or rebuilding part of a
multiple-outputs derivation, it's possible that we're
rebuilding a path that is in settings.sandbox-paths
(typically the dependencies of /bin/sh). Throw them
out. */
for (auto & i : drv->outputsAndOptPaths(worker.store)) {
/* If the name isn't known a priori (i.e. floating
content-addressed derivation), the temporary location we use
should be fresh. Freshness means it is impossible that the path
is already in the sandbox, so we don't need to worry about
removing it. */
if (i.second.second)
pathsInChroot.erase(worker.store.printStorePath(*i.second.second));
}
if (cgroup) {
if (mkdir(cgroup->c_str(), 0755) != 0)
throw SysError("creating cgroup '%s'", *cgroup);
chownToBuilder(*cgroup);
chownToBuilder(*cgroup + "/cgroup.procs");
chownToBuilder(*cgroup + "/cgroup.threads");
//chownToBuilder(*cgroup + "/cgroup.subtree_control");
}
#else
if (parsedDrv->useUidRange())
if (parsedDrv->useUidRange() && !supportsUidRange())
throw Error("feature 'uid-range' is not supported on this platform");
#if __APPLE__
/* We don't really have any parent prep work to do (yet?)
All work happens in the child, instead. */
#else
throw Error("sandboxing builds is not supported on this platform");
#endif
#endif
prepareSandbox();
} else {
if (parsedDrv->useUidRange())
throw Error("feature 'uid-range' is only supported in sandboxed builds");

17
src/libstore/build/local-derivation-goal.hh
View file

@ -324,12 +324,29 @@ struct LocalDerivationGoal : public DerivationGoal
protected:
using DerivationGoal::DerivationGoal;
/**
* Setup dependencies outside the sandbox.
* Called in the parent nix process.
*/
virtual void prepareSandbox()
{
throw Error("sandboxing builds is not supported on this platform");
};
/**
* Execute the builder, replacing the current process.
* Generally this means an `execve` call.
*/
virtual void execBuilder(std::string builder, Strings args, Strings envStrs);
/**
* Whether derivation can be built on current platform with `uid-range` feature
*/
virtual bool supportsUidRange()
{
return false;
}
};
}

6
src/libstore/platform/darwin.hh
View file

@ -42,6 +42,12 @@ public:
using LocalDerivationGoal::LocalDerivationGoal;
private:
/**
* Prepare the sandbox: This is empty on Darwin since sandbox setup happens in
* enterSandbox
*/
void prepareSandbox() override{};
/**
* Set process flags to enter or leave rosetta, then execute the builder
*/

88
src/libstore/platform/linux.cc
View file

@ -1,3 +1,4 @@
#include "build/worker.hh"
#include "cgroup.hh"
#include "gc-store.hh"
#include "signals.hh"
@ -116,6 +117,93 @@ void LinuxLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
}
void LinuxLocalDerivationGoal::prepareSandbox()
{
/* Create a temporary directory in which we set up the chroot
environment using bind-mounts. We put it in the Nix store
to ensure that we can create hard-links to non-directory
inputs in the fake Nix store in the chroot (see below). */
chrootRootDir = worker.store.Store::toRealPath(drvPath) + ".chroot";
deletePath(chrootRootDir);
/* Clean up the chroot directory automatically. */
autoDelChroot = std::make_shared<AutoDelete>(chrootRootDir);
printMsg(lvlChatty, "setting up chroot environment in '%1%'", chrootRootDir);
// FIXME: make this 0700
if (mkdir(chrootRootDir.c_str(), buildUser && buildUser->getUIDCount() != 1 ? 0755 : 0750) == -1)
throw SysError("cannot create '%1%'", chrootRootDir);
if (buildUser && chown(chrootRootDir.c_str(), buildUser->getUIDCount() != 1 ? buildUser->getUID() : 0, buildUser->getGID()) == -1)
throw SysError("cannot change ownership of '%1%'", chrootRootDir);
/* Create a writable /tmp in the chroot. Many builders need
this. (Of course they should really respect $TMPDIR
instead.) */
Path chrootTmpDir = chrootRootDir + "/tmp";
createDirs(chrootTmpDir);
chmodPath(chrootTmpDir, 01777);
/* Create a /etc/passwd with entries for the build user and the
nobody account. The latter is kind of a hack to support
Samba-in-QEMU. */
createDirs(chrootRootDir + "/etc");
if (parsedDrv->useUidRange())
chownToBuilder(chrootRootDir + "/etc");
if (parsedDrv->useUidRange() && (!buildUser || buildUser->getUIDCount() < 65536))
throw Error("feature 'uid-range' requires the setting '%s' to be enabled", settings.autoAllocateUids.name);
/* Create /etc/hosts with localhost entry. */
if (derivationType->isSandboxed())
writeFile(chrootRootDir + "/etc/hosts", "127.0.0.1 localhost\n::1 localhost\n");
/* 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. */
Path chrootStoreDir = chrootRootDir + worker.store.storeDir;
createDirs(chrootStoreDir);
chmodPath(chrootStoreDir, 01775);
if (buildUser && chown(chrootStoreDir.c_str(), 0, buildUser->getGID()) == -1)
throw SysError("cannot change ownership of '%1%'", chrootStoreDir);
for (auto & i : inputPaths) {
auto p = worker.store.printStorePath(i);
Path r = worker.store.toRealPath(p);
pathsInChroot.insert_or_assign(p, r);
}
/* If we're repairing, checking or rebuilding part of a
multiple-outputs derivation, it's possible that we're
rebuilding a path that is in settings.sandbox-paths
(typically the dependencies of /bin/sh). Throw them
out. */
for (auto & i : drv->outputsAndOptPaths(worker.store)) {
/* If the name isn't known a priori (i.e. floating
content-addressed derivation), the temporary location we use
should be fresh. Freshness means it is impossible that the path
is already in the sandbox, so we don't need to worry about
removing it. */
if (i.second.second)
pathsInChroot.erase(worker.store.printStorePath(*i.second.second));
}
if (cgroup) {
if (mkdir(cgroup->c_str(), 0755) != 0)
throw SysError("creating cgroup '%s'", *cgroup);
chownToBuilder(*cgroup);
chownToBuilder(*cgroup + "/cgroup.procs");
chownToBuilder(*cgroup + "/cgroup.threads");
//chownToBuilder(*cgroup + "/cgroup.subtree_control");
}
}
void LinuxLocalDerivationGoal::killSandbox(bool getStats)
{
if (cgroup) {

16
src/libstore/platform/linux.hh
View file

@ -42,7 +42,23 @@ public:
using LocalDerivationGoal::LocalDerivationGoal;
private:
/**
* Create and populate chroot
*/
void prepareSandbox() override;
/**
* Kill all processes by build user, possibly using a reused
* cgroup if we have one
*/
void killSandbox(bool getStatus) override;
bool supportsUidRange() override
{
return true;
}
};
}