mirror of
https://github.com/criyle/go-sandbox.git
synced 2025-11-04 14:49:53 +08:00
482 lines
14 KiB
Go
482 lines
14 KiB
Go
package forkexec
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import (
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"syscall"
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"unsafe" // required for go:linkname.
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"golang.org/x/sys/unix"
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)
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//go:linkname beforeFork syscall.runtime_BeforeFork
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func beforeFork()
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//go:linkname afterFork syscall.runtime_AfterFork
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func afterFork()
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//go:linkname afterForkInChild syscall.runtime_AfterForkInChild
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func afterForkInChild()
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// Start will fork, load seccomp and execv and being traced by ptrace
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// Return pid and potential error
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// Reference to src/syscall/exec_linux.go
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// The runtime OS thread must be locked before calling this function
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// if ptrace is set to true
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//go:norace
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func (r *Runner) Start() (int, error) {
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var (
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err1, err2 syscall.Errno
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r1 uintptr
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unshareUser = r.UnshareFlags&unix.CLONE_NEWUSER == unix.CLONE_NEWUSER
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)
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argv0, argv, envv, err := prepareExec(r.Args, r.Env)
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if err != nil {
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return 0, err
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}
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// prepare work dir
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workdir, err := syscallStringFromString(r.WorkDir)
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if err != nil {
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return 0, err
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}
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// prepare hostname
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hostname, err := syscallStringFromString(r.HostName)
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if err != nil {
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return 0, err
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}
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// prepare domainname
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domainname, err := syscallStringFromString(r.DomainName)
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if err != nil {
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return 0, err
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}
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// prepare pivot_root param
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pivotRoot, oldRoot, err := preparePivotRoot(r.PivotRoot)
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if err != nil {
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return 0, err
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}
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// socketpair p used to notify child the uid / gid mapping have been setup
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// socketpair p is also used to sync with parent before final execve
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// p[0] is used by parent and p[1] is used by child
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p, err := syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM|syscall.SOCK_CLOEXEC, 0)
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if err != nil {
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return 0, err
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}
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// similar to exec_linux, avoid side effect by shuffling around
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fd, nextfd := prepareFds(r.Files)
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pipe := p[1]
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// Acquire the fork lock so that no other threads
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// create new fds that are not yet close-on-exec
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// before we fork.
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syscall.ForkLock.Lock()
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// About to call fork.
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// No more allocation or calls of non-assembly functions.
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beforeFork()
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// UnshareFlags (new namespaces) is activated by clone syscall
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pid, _, err1 := syscall.RawSyscall6(syscall.SYS_CLONE, uintptr(syscall.SIGCHLD)|(r.UnshareFlags&UnshareFlags), 0, 0, 0, 0, 0)
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if err1 != 0 || pid != 0 {
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// restore all signals
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afterFork()
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syscall.ForkLock.Unlock()
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// sync with child
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unix.Close(p[1])
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// clone syscall failed
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if err1 != 0 {
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unix.Close(p[0])
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return int(pid), syscall.Errno(err1)
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}
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// synchronize with child for uid / gid map
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if unshareUser {
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if err = writeIDMaps(int(pid)); err != nil {
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err2 = err.(syscall.Errno)
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}
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syscall.RawSyscall(syscall.SYS_WRITE, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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}
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_READ, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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// child returned error code
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if r1 != unsafe.Sizeof(err2) || err2 != 0 || err1 != 0 {
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unix.Close(p[0])
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if r1 == unsafe.Sizeof(err2) {
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err = syscall.Errno(err2)
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}
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if err == nil {
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err = syscall.EPIPE
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}
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handleChildFailed(pid)
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return 0, err
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}
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if r.SyncFunc != nil {
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err = r.SyncFunc(int(pid))
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}
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// if syncfunc return error, then fail child immediately. Otherwise, ack child (err1 == 0)
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if err == nil {
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syscall.RawSyscall(syscall.SYS_WRITE, uintptr(p[0]), uintptr(unsafe.Pointer(&err1)), uintptr(unsafe.Sizeof((err1))))
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} else {
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unix.Close(p[0])
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handleChildFailed(pid)
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return 0, err
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}
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// if stopped before execve, then do not wait until execve
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if r.Ptrace && r.Seccomp != nil || r.StopBeforeSeccomp {
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unix.Close(p[0])
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return int(pid), nil
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}
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// if read anything mean child failed after sync (close_on_exec so it should not block)
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_READ, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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unix.Close(p[0])
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if r1 != 0 || err1 != 0 {
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if r1 == unsafe.Sizeof(err2) {
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err = syscall.Errno(err2)
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}
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if err == nil {
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err = syscall.EPIPE
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}
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handleChildFailed(pid)
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return 0, err
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}
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return int(pid), nil
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}
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// In child process
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afterForkInChild()
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// Notice: cannot call any GO functions beyond this point
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// If usernamespace is unshared, uid map and gid map is required to create folders
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// and files
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// We need parent to setup uid_map / gid_map for us since we do not have capabilities
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// in the original namespace
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// At the same time, socket pair / pipe sychronization is required as well
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if _, _, err1 = syscall.RawSyscall(syscall.SYS_CLOSE, uintptr(p[0]), 0, 0); err1 != 0 {
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goto childerror
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}
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if unshareUser {
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_READ, uintptr(pipe), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2))
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if err1 != 0 {
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goto childerror
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}
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if r1 != unsafe.Sizeof(err2) {
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err1 = syscall.EINVAL
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goto childerror
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}
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if err2 != 0 {
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err1 = err2
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goto childerror
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}
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}
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// Get pid of child
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pid, _, err1 = syscall.RawSyscall(syscall.SYS_GETPID, 0, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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// Pass 1 & pass 2 assigns fds for child process
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// Pass 1: fd[i] < i => nextfd
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if pipe < nextfd {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_DUP3, uintptr(pipe), uintptr(nextfd), syscall.O_CLOEXEC)
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if err1 != 0 {
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goto childerror
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}
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pipe = nextfd
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nextfd++
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}
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if r.ExecFile > 0 && int(r.ExecFile) < nextfd {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_DUP3, r.ExecFile, uintptr(nextfd), syscall.O_CLOEXEC)
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if err1 != 0 {
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goto childerror
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}
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r.ExecFile = uintptr(nextfd)
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nextfd++
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}
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for i := 0; i < len(fd); i++ {
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// Avoid fd rewrite
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for nextfd == i || (r.ExecFile > 0 && nextfd == int(r.ExecFile)) {
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nextfd++
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}
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if fd[i] >= 0 && fd[i] < int(i) {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), syscall.O_CLOEXEC)
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if err1 != 0 {
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goto childerror
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}
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// Set up close on exec
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fd[i] = nextfd
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nextfd++
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}
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}
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// Pass 2: fd[i] => i
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for i := 0; i < len(fd); i++ {
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if fd[i] == -1 {
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syscall.RawSyscall(syscall.SYS_CLOSE, uintptr(i), 0, 0)
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continue
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}
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if fd[i] == int(i) {
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// dup2(i, i) will not clear close on exec flag, need to reset the flag
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_, _, err1 = syscall.RawSyscall(syscall.SYS_FCNTL, uintptr(fd[i]), syscall.F_SETFD, 0)
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if err1 != 0 {
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goto childerror
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}
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continue
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}
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_, _, err1 = syscall.RawSyscall(syscall.SYS_DUP3, uintptr(fd[i]), uintptr(i), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Set the pgid, so that the wait operation can apply to only certain
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// subgroup of processes
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_, _, err1 = syscall.RawSyscall(syscall.SYS_SETPGID, 0, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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// If mount point is unshared, mark root as private to avoid propagate
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// outside to the original mount namespace
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if r.UnshareFlags&syscall.CLONE_NEWNS == syscall.CLONE_NEWNS {
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_MOUNT, uintptr(unsafe.Pointer(&none[0])),
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uintptr(unsafe.Pointer(&slash[0])), 0, syscall.MS_REC|syscall.MS_PRIVATE, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// mount tmpfs & chdir to new root before performing mounts
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if pivotRoot != nil {
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// mount("tmpfs", root, "tmpfs", 0, "")
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_MOUNT, uintptr(unsafe.Pointer(&tmpfs[0])),
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uintptr(unsafe.Pointer(pivotRoot)), uintptr(unsafe.Pointer(&tmpfs[0])), 0,
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uintptr(unsafe.Pointer(&empty[0])), 0)
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if err1 != 0 {
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goto childerror
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}
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_, _, err1 = syscall.RawSyscall(syscall.SYS_CHDIR, uintptr(unsafe.Pointer(pivotRoot)), 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// performing mounts
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for _, m := range r.Mounts {
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// mkdirs(target)
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for _, p := range m.Prefixes {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_MKDIRAT, uintptr(_AT_FDCWD), uintptr(unsafe.Pointer(p)), 0755)
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if err1 != 0 && err1 != syscall.EEXIST {
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goto childerror
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}
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}
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// mount(source, target, fsType, flags, data)
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_MOUNT, uintptr(unsafe.Pointer(m.Source)),
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uintptr(unsafe.Pointer(m.Target)), uintptr(unsafe.Pointer(m.FsType)), uintptr(m.Flags),
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uintptr(unsafe.Pointer(m.Data)), 0)
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if err1 != 0 {
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goto childerror
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}
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// bind mount is not respect ro flag so that read-only bind mount needs remount
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if m.Flags&bindRo == bindRo {
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_MOUNT, uintptr(unsafe.Pointer(&empty[0])),
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uintptr(unsafe.Pointer(m.Target)), uintptr(unsafe.Pointer(m.FsType)),
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uintptr(m.Flags|syscall.MS_REMOUNT), uintptr(unsafe.Pointer(m.Data)), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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}
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// pivit_root
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if pivotRoot != nil {
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// mkdir("old_root")
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_, _, err1 = syscall.RawSyscall(syscall.SYS_MKDIRAT, uintptr(_AT_FDCWD), uintptr(unsafe.Pointer(oldRoot)), 0755)
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if err1 != 0 {
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goto childerror
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}
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// pivot_root(root, "old_root")
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_, _, err1 = syscall.RawSyscall(syscall.SYS_PIVOT_ROOT, uintptr(unsafe.Pointer(pivotRoot)), uintptr(unsafe.Pointer(oldRoot)), 0)
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if err1 != 0 {
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goto childerror
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}
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// umount("old_root", MNT_DETACH)
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_, _, err1 = syscall.RawSyscall(syscall.SYS_UMOUNT2, uintptr(unsafe.Pointer(oldRoot)), syscall.MNT_DETACH, 0)
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if err1 != 0 {
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goto childerror
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}
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// rmdir("old_root")
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_, _, err1 = syscall.RawSyscall(syscall.SYS_UNLINKAT, uintptr(_AT_FDCWD), uintptr(unsafe.Pointer(oldRoot)), uintptr(unix.AT_REMOVEDIR))
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if err1 != 0 {
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goto childerror
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}
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// mount("tmpfs", "/", "tmpfs", MS_BIND | MS_REMOUNT | MS_RDONLY | MS_NOATIME | MS_NOSUID, nil)
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_MOUNT, uintptr(unsafe.Pointer(&tmpfs[0])),
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uintptr(unsafe.Pointer(&slash[0])), uintptr(unsafe.Pointer(&tmpfs[0])),
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uintptr(syscall.MS_BIND|syscall.MS_REMOUNT|syscall.MS_RDONLY|syscall.MS_NOATIME|syscall.MS_NOSUID),
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uintptr(unsafe.Pointer(&empty[0])), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// SetHostName
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if hostname != nil {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_SETHOSTNAME,
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uintptr(unsafe.Pointer(hostname)), uintptr(len(r.HostName)), 0)
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}
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// SetDomainName
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if domainname != nil {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_SETDOMAINNAME,
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uintptr(unsafe.Pointer(domainname)), uintptr(len(r.DomainName)), 0)
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}
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// chdir for child
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if workdir != nil {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_CHDIR, uintptr(unsafe.Pointer(workdir)), 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Set limit
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for _, rlim := range r.RLimits {
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// Prlimit instead of setrlimit to avoid 32-bit limitation (linux > 3.2)
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_PRLIMIT64, 0, uintptr(rlim.Res), uintptr(unsafe.Pointer(&rlim.Rlim)), 0, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// No new privs
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if r.NoNewPrivs || r.Seccomp != nil {
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_, _, err1 = syscall.RawSyscall6(syscall.SYS_PRCTL, unix.PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Drop all capabilities
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if r.DropCaps {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_CAPSET, uintptr(unsafe.Pointer(&dropCapHeader)), uintptr(unsafe.Pointer(&dropCapData)), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Enable Ptrace & sync with parent (since ptrace_me is a blocking operation)
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if r.Ptrace && r.Seccomp != nil {
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err2 = 0
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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if r1 == 0 || err1 != 0 {
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goto childerror
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}
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_READ, uintptr(pipe), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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if r1 == 0 || err1 != 0 {
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goto childerror
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}
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_, _, err1 = syscall.RawSyscall(syscall.SYS_PTRACE, uintptr(syscall.PTRACE_TRACEME), 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// if both seccomp and ptrace is defined, then seccomp filter should have
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// traced execve, thus child need parent attached to it first
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// actually, this is not effective if pid namespace is unshared
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if r.StopBeforeSeccomp || (r.Seccomp != nil && r.Ptrace) {
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// Stop to wait for ptrace tracer
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_, _, err1 = syscall.RawSyscall(syscall.SYS_KILL, pid, uintptr(syscall.SIGSTOP), 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// Load seccomp, stop and wait for tracer
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if r.Seccomp != nil {
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// If execve is seccomp trapped, then tracee stop is necessary
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// otherwise execve will fail due to ENOSYS
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// Do getpid and kill to send SYS_KILL to self
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// need to do before seccomp as these might be traced
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// Load seccomp filter
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_, _, err1 = syscall.RawSyscall(unix.SYS_SECCOMP, SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_TSYNC, uintptr(unsafe.Pointer(r.Seccomp)))
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if err1 != 0 {
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goto childerror
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}
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}
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// Before exec, sync with parent through pipe (configured as close_on_exec)
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if !r.Ptrace || r.Seccomp == nil {
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err2 = 0
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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if r1 == 0 || err1 != 0 {
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goto childerror
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}
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r1, _, err1 = syscall.RawSyscall(syscall.SYS_READ, uintptr(pipe), uintptr(unsafe.Pointer(&err2)), uintptr(unsafe.Sizeof(err2)))
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if r1 == 0 || err1 != 0 {
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goto childerror
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}
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}
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// Enable ptrace if no seccomp is needed
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if r.Ptrace && r.Seccomp == nil {
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_, _, err1 = syscall.RawSyscall(syscall.SYS_PTRACE, uintptr(syscall.PTRACE_TRACEME), 0, 0)
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if err1 != 0 {
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goto childerror
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}
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}
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// at this point, runner is successfully attached for seccomp trap filter
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// or execve traped without seccomp filter
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// time to exec
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// if execfile fd is specified, call fexecve
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if r.ExecFile > 0 {
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_, _, err1 = syscall.RawSyscall6(unix.SYS_EXECVEAT, r.ExecFile,
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uintptr(unsafe.Pointer(&empty[0])),
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uintptr(unsafe.Pointer(&argv[0])),
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uintptr(unsafe.Pointer(&envv[0])), unix.AT_EMPTY_PATH, 0)
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} else {
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_, _, err1 = syscall.RawSyscall6(unix.SYS_EXECVEAT, uintptr(_AT_FDCWD),
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uintptr(unsafe.Pointer(argv0)),
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uintptr(unsafe.Pointer(&argv[0])),
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uintptr(unsafe.Pointer(&envv[0])), 0, 0)
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}
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childerror:
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// send error code on pipe
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syscall.RawSyscall(unix.SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
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for {
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syscall.RawSyscall(syscall.SYS_EXIT, uintptr(err1+err2), 0, 0)
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}
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// cannot reach this point
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}
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func handleChildFailed(pid uintptr) {
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var wstatus syscall.WaitStatus
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// make sure not blocked
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unix.Kill(int(pid), syscall.SIGKILL)
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// child failed; wait for it to exit, to make sure the zombies don't accumulate
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_, err3 := syscall.Wait4(int(pid), &wstatus, 0, nil)
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for err3 == syscall.EINTR {
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_, err3 = syscall.Wait4(int(pid), &wstatus, 0, nil)
|
|
}
|
|
}
|