package ebpf
import (
"errors"
"fmt"
"os"
"runtime"
"sync"
"unsafe"
"github.com/cilium/ebpf"
"github.com/cilium/ebpf/asm"
"github.com/cilium/ebpf/link"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
func nilCloser() error {
return nil
}
func findAttachedCgroupDeviceFilters(dirFd int) ([]*ebpf.Program, error) {
type bpfAttrQuery struct {
TargetFd uint32
AttachType uint32
QueryType uint32
AttachFlags uint32
ProgIds uint64 // __aligned_u64
ProgCnt uint32
}
// Currently you can only have 64 eBPF programs attached to a cgroup.
size := 64
retries := 0
for retries < 10 {
progIds := make([]uint32, size)
query := bpfAttrQuery{
TargetFd: uint32(dirFd),
AttachType: uint32(unix.BPF_CGROUP_DEVICE),
ProgIds: uint64(uintptr(unsafe.Pointer(&progIds[0]))),
ProgCnt: uint32(len(progIds)),
}
// Fetch the list of program ids.
_, _, errno := unix.Syscall(unix.SYS_BPF,
uintptr(unix.BPF_PROG_QUERY),
uintptr(unsafe.Pointer(&query)),
unsafe.Sizeof(query))
size = int(query.ProgCnt)
runtime.KeepAlive(query)
if errno != 0 {
// On ENOSPC we get the correct number of programs.
if errno == unix.ENOSPC {
retries++
continue
}
return nil, fmt.Errorf("bpf_prog_query(BPF_CGROUP_DEVICE) failed: %w", errno)
}
// Convert the ids to program handles.
progIds = progIds[:size]
programs := make([]*ebpf.Program, 0, len(progIds))
for _, progId := range progIds {
program, err := ebpf.NewProgramFromID(ebpf.ProgramID(progId))
if err != nil {
// We skip over programs that give us -EACCES or -EPERM. This
// is necessary because there may be BPF programs that have
// been attached (such as with --systemd-cgroup) which have an
// LSM label that blocks us from interacting with the program.
//
// Because additional BPF_CGROUP_DEVICE programs only can add
// restrictions, there's no real issue with just ignoring these
// programs (and stops runc from breaking on distributions with
// very strict SELinux policies).
if errors.Is(err, os.ErrPermission) {
logrus.Debugf("ignoring existing CGROUP_DEVICE program (prog_id=%v) which cannot be accessed by runc -- likely due to LSM policy: %v", progId, err)
continue
}
return nil, fmt.Errorf("cannot fetch program from id: %w", err)
}
programs = append(programs, program)
}
runtime.KeepAlive(progIds)
return programs, nil
}
return nil, errors.New("could not get complete list of CGROUP_DEVICE programs")
}
var (
haveBpfProgReplaceBool bool
haveBpfProgReplaceOnce sync.Once
)
// Loosely based on the BPF_F_REPLACE support check in
// https://github.com/cilium/ebpf/blob/v0.6.0/link/syscalls.go.
//
// TODO: move this logic to cilium/ebpf
func haveBpfProgReplace() bool {
haveBpfProgReplaceOnce.Do(func() {
prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
Type: ebpf.CGroupDevice,
License: "MIT",
Instructions: asm.Instructions{
asm.Mov.Imm(asm.R0, 0),
asm.Return(),
},
})
if err != nil {
logrus.Debugf("checking for BPF_F_REPLACE support: ebpf.NewProgram failed: %v", err)
return
}
defer prog.Close()
devnull, err := os.Open("/dev/null")
if err != nil {
logrus.Debugf("checking for BPF_F_REPLACE support: open dummy target fd: %v", err)
return
}
defer devnull.Close()
// We know that we have BPF_PROG_ATTACH since we can load
// BPF_CGROUP_DEVICE programs. If passing BPF_F_REPLACE gives us EINVAL
// we know that the feature isn't present.
err = link.RawAttachProgram(link.RawAttachProgramOptions{
// We rely on this fd being checked after attachFlags.
Target: int(devnull.Fd()),
// Attempt to "replace" bad fds with this program.
Program: prog,
Attach: ebpf.AttachCGroupDevice,
Flags: unix.BPF_F_ALLOW_MULTI | unix.BPF_F_REPLACE,
})
if errors.Is(err, unix.EINVAL) {
// not supported
return
}
// attach_flags test succeeded.
if !errors.Is(err, unix.EBADF) {
logrus.Debugf("checking for BPF_F_REPLACE: got unexpected (not EBADF or EINVAL) error: %v", err)
}
haveBpfProgReplaceBool = true
})
return haveBpfProgReplaceBool
}
// LoadAttachCgroupDeviceFilter installs eBPF device filter program to /sys/fs/cgroup/<foo> directory.
//
// Requires the system to be running in cgroup2 unified-mode with kernel >= 4.15 .
//
// https://github.com/torvalds/linux/commit/ebc614f687369f9df99828572b1d85a7c2de3d92
func LoadAttachCgroupDeviceFilter(insts asm.Instructions, license string, dirFd int) (func() error, error) {
// Increase `ulimit -l` limit to avoid BPF_PROG_LOAD error (#2167).
// This limit is not inherited into the container.
memlockLimit := &unix.Rlimit{
Cur: unix.RLIM_INFINITY,
Max: unix.RLIM_INFINITY,
}
_ = unix.Setrlimit(unix.RLIMIT_MEMLOCK, memlockLimit)
// Get the list of existing programs.
oldProgs, err := findAttachedCgroupDeviceFilters(dirFd)
if err != nil {
return nilCloser, err
}
useReplaceProg := haveBpfProgReplace() && len(oldProgs) == 1
// Generate new program.
spec := &ebpf.ProgramSpec{
Type: ebpf.CGroupDevice,
Instructions: insts,
License: license,
}
prog, err := ebpf.NewProgram(spec)
if err != nil {
return nilCloser, err
}
// If there is only one old program, we can just replace it directly.
var (
replaceProg *ebpf.Program
attachFlags uint32 = unix.BPF_F_ALLOW_MULTI
)
if useReplaceProg {
replaceProg = oldProgs[0]
attachFlags |= unix.BPF_F_REPLACE
}
err = link.RawAttachProgram(link.RawAttachProgramOptions{
Target: dirFd,
Program: prog,
Replace: replaceProg,
Attach: ebpf.AttachCGroupDevice,
Flags: attachFlags,
})
if err != nil {
return nilCloser, fmt.Errorf("failed to call BPF_PROG_ATTACH (BPF_CGROUP_DEVICE, BPF_F_ALLOW_MULTI): %w", err)
}
closer := func() error {
err = link.RawDetachProgram(link.RawDetachProgramOptions{
Target: dirFd,
Program: prog,
Attach: ebpf.AttachCGroupDevice,
})
if err != nil {
return fmt.Errorf("failed to call BPF_PROG_DETACH (BPF_CGROUP_DEVICE): %w", err)
}
// TODO: Should we attach the old filters back in this case? Otherwise
// we fail-open on a security feature, which is a bit scary.
return nil
}
if !useReplaceProg {
logLevel := logrus.DebugLevel
// If there was more than one old program, give a warning (since this
// really shouldn't happen with runc-managed cgroups) and then detach
// all the old programs.
if len(oldProgs) > 1 {
// NOTE: Ideally this should be a warning but it turns out that
// systemd-managed cgroups trigger this warning (apparently
// systemd doesn't delete old non-systemd programs when
// setting properties).
logrus.Infof("found more than one filter (%d) attached to a cgroup -- removing extra filters!", len(oldProgs))
logLevel = logrus.InfoLevel
}
for idx, oldProg := range oldProgs {
// Output some extra debug info.
if info, err := oldProg.Info(); err == nil {
fields := logrus.Fields{
"type": info.Type.String(),
"tag": info.Tag,
"name": info.Name,
}
if id, ok := info.ID(); ok {
fields["id"] = id
}
if runCount, ok := info.RunCount(); ok {
fields["run_count"] = runCount
}
if runtime, ok := info.Runtime(); ok {
fields["runtime"] = runtime.String()
}
logrus.WithFields(fields).Logf(logLevel, "removing old filter %d from cgroup", idx)
}
err = link.RawDetachProgram(link.RawDetachProgramOptions{
Target: dirFd,
Program: oldProg,
Attach: ebpf.AttachCGroupDevice,
})
if err != nil {
return closer, fmt.Errorf("failed to call BPF_PROG_DETACH (BPF_CGROUP_DEVICE) on old filter program: %w", err)
}
}
}
return closer, nil
}
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