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Split auto UID allocation from cgroups

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Cgroups are now only used for derivations that require the uid-range
range feature. This allows auto UID allocation even on systems that
don't have cgroups (like macOS).

Also, make things work on modern systems that use cgroups v2 (where
there is a single hierarchy and no "systemd" controller).
This commit is contained in:
Eelco Dolstra 2022-11-08 16:03:42 +01:00
parent 40911d7dec
commit 2fde7e0108
9 changed files with 122 additions and 96 deletions
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149
src/libstore/lock.cc
View file

@ -20,12 +20,8 @@ struct SimpleUserLock : UserLock
killUser(uid);
}
std::pair<uid_t, uid_t> getUIDRange() override
{
assert(uid);
return {uid, uid};
}
uid_t getUID() override { assert(uid); return uid; }
uid_t getUIDCount() override { return 1; }
gid_t getGID() override { assert(gid); return gid; }
std::vector<gid_t> getSupplementaryGIDs() override { return supplementaryGIDs; }
@ -115,48 +111,65 @@ struct SimpleUserLock : UserLock
}
};
#if __linux__
struct CgroupUserLock : UserLock
struct AutoUserLock : UserLock
{
AutoCloseFD fdUserLock;
uid_t uid;
uid_t firstUid = 0;
uid_t nrIds = 1;
#if __linux__
std::optional<Path> cgroup;
#endif
~AutoUserLock()
{
// Get rid of our cgroup, ignoring errors.
if (cgroup) rmdir(cgroup->c_str());
}
void kill() override
{
#if __linux__
if (cgroup) {
printError("KILL CGROUP %s", *cgroup);
destroyCgroup(*cgroup);
cgroup.reset();
if (mkdir(cgroup->c_str(), 0755) == -1)
throw SysError("creating cgroup '%s'", *cgroup);
} else
#endif
{
assert(firstUid);
printError("KILL USER %d", firstUid);
killUser(firstUid);
}
}
std::pair<uid_t, uid_t> getUIDRange() override
{
assert(uid);
return {uid, uid + settings.idsPerBuild - 1};
}
uid_t getUID() override { assert(firstUid); return firstUid; }
gid_t getUIDCount() override { return nrIds; }
gid_t getGID() override
{
// We use the same GID ranges as for the UIDs.
assert(uid);
return uid;
assert(firstUid);
return firstUid;
}
std::vector<gid_t> getSupplementaryGIDs() override { return {}; }
static std::unique_ptr<UserLock> acquire()
static std::unique_ptr<UserLock> acquire(uid_t nrIds)
{
settings.requireExperimentalFeature(Xp::AutoAllocateUids);
assert(settings.startId > 0);
assert(settings.startId % settings.idsPerBuild == 0);
assert(settings.uidCount % settings.idsPerBuild == 0);
assert(settings.startId % maxIdsPerBuild == 0);
assert(settings.uidCount % maxIdsPerBuild == 0);
assert((uint64_t) settings.startId + (uint64_t) settings.uidCount <= std::numeric_limits<uid_t>::max());
assert(nrIds <= maxIdsPerBuild);
// FIXME: check whether the id range overlaps any known users
createDirs(settings.nixStateDir + "/userpool2");
size_t nrSlots = settings.uidCount / settings.idsPerBuild;
size_t nrSlots = settings.uidCount / maxIdsPerBuild;
for (size_t i = 0; i < nrSlots; i++) {
debug("trying user slot '%d'", i);
@ -170,11 +183,47 @@ struct CgroupUserLock : UserLock
throw SysError("opening user lock '%s'", fnUserLock);
if (lockFile(fd.get(), ltWrite, false)) {
auto lock = std::make_unique<CgroupUserLock>();
auto s = drainFD(fd.get());
#if __linux__
if (s != "") {
/* Kill the old cgroup, to ensure there are no
processes left over from an interrupted build. */
destroyCgroup(s);
}
#endif
if (ftruncate(fd.get(), 0) == -1)
throw Error("truncating user lock");
auto lock = std::make_unique<AutoUserLock>();
lock->fdUserLock = std::move(fd);
lock->uid = settings.startId + i * settings.idsPerBuild;
auto s = drainFD(lock->fdUserLock.get());
if (s != "") lock->cgroup = s;
lock->firstUid = settings.startId + i * maxIdsPerBuild;
lock->nrIds = nrIds;
if (nrIds > 1) {
auto ourCgroups = getCgroups("/proc/self/cgroup");
auto ourCgroup = ourCgroups[""];
if (ourCgroup == "")
throw Error("cannot determine cgroup name from /proc/self/cgroup");
auto ourCgroupPath = canonPath("/sys/fs/cgroup/" + ourCgroup);
printError("PARENT CGROUP = %s", ourCgroupPath);
if (!pathExists(ourCgroupPath))
throw Error("expected cgroup directory '%s'", ourCgroupPath);
lock->cgroup = fmt("%s/nix-build-%d", ourCgroupPath, lock->firstUid);
printError("CHILD CGROUP = %s", *lock->cgroup);
/* Record the cgroup in the lock file. This ensures that
if we subsequently get executed under a different parent
cgroup, we kill the previous cgroup first. */
writeFull(lock->fdUserLock.get(), *lock->cgroup);
}
return lock;
}
}
@ -182,50 +231,16 @@ struct CgroupUserLock : UserLock
return nullptr;
}
std::optional<Path> cgroup;
std::optional<Path> getCgroup() override
{
if (!cgroup) {
/* Create a systemd cgroup since that's the minimum
required by systemd-nspawn. */
auto ourCgroups = getCgroups("/proc/self/cgroup");
auto systemdCgroup = ourCgroups["systemd"];
if (systemdCgroup == "")
throw Error("'systemd' cgroup does not exist");
auto hostCgroup = canonPath("/sys/fs/cgroup/systemd/" + systemdCgroup);
if (!pathExists(hostCgroup))
throw Error("expected cgroup directory '%s'", hostCgroup);
cgroup = fmt("%s/nix-%d", hostCgroup, uid);
destroyCgroup(*cgroup);
if (mkdir(cgroup->c_str(), 0755) == -1)
throw SysError("creating cgroup '%s'", *cgroup);
/* Record the cgroup in the lock file. This ensures that
if we subsequently get executed under a different parent
cgroup, we kill the previous cgroup first. */
if (ftruncate(fdUserLock.get(), 0) == -1)
throw Error("truncating user lock");
writeFull(fdUserLock.get(), *cgroup);
}
return cgroup;
};
};
#endif
std::unique_ptr<UserLock> acquireUserLock()
{
#if __linux__
if (settings.autoAllocateUids)
return CgroupUserLock::acquire();
else
std::optional<Path> getCgroup() override { return cgroup; }
#endif
};
std::unique_ptr<UserLock> acquireUserLock(uid_t nrIds)
{
if (settings.autoAllocateUids)
return AutoUserLock::acquire(nrIds);
else
return SimpleUserLock::acquire();
}