diff options
Diffstat (limited to '')
| -rw-r--r-- | src/syscall/exec_linux.go | 719 |
1 files changed, 719 insertions, 0 deletions
diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go new file mode 100644 index 0000000..dfbb38a --- /dev/null +++ b/src/syscall/exec_linux.go @@ -0,0 +1,719 @@ +// Copyright 2011 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +//go:build linux + +package syscall + +import ( + "internal/itoa" + "runtime" + "unsafe" +) + +// Linux unshare/clone/clone2/clone3 flags, architecture-independent, +// copied from linux/sched.h. +const ( + CLONE_VM = 0x00000100 // set if VM shared between processes + CLONE_FS = 0x00000200 // set if fs info shared between processes + CLONE_FILES = 0x00000400 // set if open files shared between processes + CLONE_SIGHAND = 0x00000800 // set if signal handlers and blocked signals shared + CLONE_PIDFD = 0x00001000 // set if a pidfd should be placed in parent + CLONE_PTRACE = 0x00002000 // set if we want to let tracing continue on the child too + CLONE_VFORK = 0x00004000 // set if the parent wants the child to wake it up on mm_release + CLONE_PARENT = 0x00008000 // set if we want to have the same parent as the cloner + CLONE_THREAD = 0x00010000 // Same thread group? + CLONE_NEWNS = 0x00020000 // New mount namespace group + CLONE_SYSVSEM = 0x00040000 // share system V SEM_UNDO semantics + CLONE_SETTLS = 0x00080000 // create a new TLS for the child + CLONE_PARENT_SETTID = 0x00100000 // set the TID in the parent + CLONE_CHILD_CLEARTID = 0x00200000 // clear the TID in the child + CLONE_DETACHED = 0x00400000 // Unused, ignored + CLONE_UNTRACED = 0x00800000 // set if the tracing process can't force CLONE_PTRACE on this clone + CLONE_CHILD_SETTID = 0x01000000 // set the TID in the child + CLONE_NEWCGROUP = 0x02000000 // New cgroup namespace + CLONE_NEWUTS = 0x04000000 // New utsname namespace + CLONE_NEWIPC = 0x08000000 // New ipc namespace + CLONE_NEWUSER = 0x10000000 // New user namespace + CLONE_NEWPID = 0x20000000 // New pid namespace + CLONE_NEWNET = 0x40000000 // New network namespace + CLONE_IO = 0x80000000 // Clone io context + + // Flags for the clone3() syscall. + + CLONE_CLEAR_SIGHAND = 0x100000000 // Clear any signal handler and reset to SIG_DFL. + CLONE_INTO_CGROUP = 0x200000000 // Clone into a specific cgroup given the right permissions. + + // Cloning flags intersect with CSIGNAL so can be used with unshare and clone3 + // syscalls only: + + CLONE_NEWTIME = 0x00000080 // New time namespace +) + +// SysProcIDMap holds Container ID to Host ID mappings used for User Namespaces in Linux. +// See user_namespaces(7). +type SysProcIDMap struct { + ContainerID int // Container ID. + HostID int // Host ID. + Size int // Size. +} + +type SysProcAttr struct { + Chroot string // Chroot. + Credential *Credential // Credential. + // Ptrace tells the child to call ptrace(PTRACE_TRACEME). + // Call runtime.LockOSThread before starting a process with this set, + // and don't call UnlockOSThread until done with PtraceSyscall calls. + Ptrace bool + Setsid bool // Create session. + // Setpgid sets the process group ID of the child to Pgid, + // or, if Pgid == 0, to the new child's process ID. + Setpgid bool + // Setctty sets the controlling terminal of the child to + // file descriptor Ctty. Ctty must be a descriptor number + // in the child process: an index into ProcAttr.Files. + // This is only meaningful if Setsid is true. + Setctty bool + Noctty bool // Detach fd 0 from controlling terminal + Ctty int // Controlling TTY fd + // Foreground places the child process group in the foreground. + // This implies Setpgid. The Ctty field must be set to + // the descriptor of the controlling TTY. + // Unlike Setctty, in this case Ctty must be a descriptor + // number in the parent process. + Foreground bool + Pgid int // Child's process group ID if Setpgid. + // Pdeathsig, if non-zero, is a signal that the kernel will send to + // the child process when the creating thread dies. Note that the signal + // is sent on thread termination, which may happen before process termination. + // There are more details at https://go.dev/issue/27505. + Pdeathsig Signal + Cloneflags uintptr // Flags for clone calls (Linux only) + Unshareflags uintptr // Flags for unshare calls (Linux only) + UidMappings []SysProcIDMap // User ID mappings for user namespaces. + GidMappings []SysProcIDMap // Group ID mappings for user namespaces. + // GidMappingsEnableSetgroups enabling setgroups syscall. + // If false, then setgroups syscall will be disabled for the child process. + // This parameter is no-op if GidMappings == nil. Otherwise for unprivileged + // users this should be set to false for mappings work. + GidMappingsEnableSetgroups bool + AmbientCaps []uintptr // Ambient capabilities (Linux only) + UseCgroupFD bool // Whether to make use of the CgroupFD field. + CgroupFD int // File descriptor of a cgroup to put the new process into. +} + +var ( + none = [...]byte{'n', 'o', 'n', 'e', 0} + slash = [...]byte{'/', 0} +) + +// Implemented in runtime package. +func runtime_BeforeFork() +func runtime_AfterFork() +func runtime_AfterForkInChild() + +// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child. +// If a dup or exec fails, write the errno error to pipe. +// (Pipe is close-on-exec so if exec succeeds, it will be closed.) +// In the child, this function must not acquire any locks, because +// they might have been locked at the time of the fork. This means +// no rescheduling, no malloc calls, and no new stack segments. +// For the same reason compiler does not race instrument it. +// The calls to RawSyscall are okay because they are assembly +// functions that do not grow the stack. +// +//go:norace +func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) { + // Set up and fork. This returns immediately in the parent or + // if there's an error. + upid, err, mapPipe, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe) + if locked { + runtime_AfterFork() + } + if err != 0 { + return 0, err + } + + // parent; return PID + pid = int(upid) + + if sys.UidMappings != nil || sys.GidMappings != nil { + Close(mapPipe[0]) + var err2 Errno + // uid/gid mappings will be written after fork and unshare(2) for user + // namespaces. + if sys.Unshareflags&CLONE_NEWUSER == 0 { + if err := writeUidGidMappings(pid, sys); err != nil { + err2 = err.(Errno) + } + } + RawSyscall(SYS_WRITE, uintptr(mapPipe[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) + Close(mapPipe[1]) + } + + return pid, 0 +} + +const _LINUX_CAPABILITY_VERSION_3 = 0x20080522 + +type capHeader struct { + version uint32 + pid int32 +} + +type capData struct { + effective uint32 + permitted uint32 + inheritable uint32 +} +type caps struct { + hdr capHeader + data [2]capData +} + +// See CAP_TO_INDEX in linux/capability.h: +func capToIndex(cap uintptr) uintptr { return cap >> 5 } + +// See CAP_TO_MASK in linux/capability.h: +func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) } + +// cloneArgs holds arguments for clone3 Linux syscall. +type cloneArgs struct { + flags uint64 // Flags bit mask + pidFD uint64 // Where to store PID file descriptor (int *) + childTID uint64 // Where to store child TID, in child's memory (pid_t *) + parentTID uint64 // Where to store child TID, in parent's memory (pid_t *) + exitSignal uint64 // Signal to deliver to parent on child termination + stack uint64 // Pointer to lowest byte of stack + stackSize uint64 // Size of stack + tls uint64 // Location of new TLS + setTID uint64 // Pointer to a pid_t array (since Linux 5.5) + setTIDSize uint64 // Number of elements in set_tid (since Linux 5.5) + cgroup uint64 // File descriptor for target cgroup of child (since Linux 5.7) +} + +// forkAndExecInChild1 implements the body of forkAndExecInChild up to +// the parent's post-fork path. This is a separate function so we can +// separate the child's and parent's stack frames if we're using +// vfork. +// +// This is go:noinline because the point is to keep the stack frames +// of this and forkAndExecInChild separate. +// +//go:noinline +//go:norace +//go:nocheckptr +func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid uintptr, err1 Errno, mapPipe [2]int, locked bool) { + // Defined in linux/prctl.h starting with Linux 4.3. + const ( + PR_CAP_AMBIENT = 0x2f + PR_CAP_AMBIENT_RAISE = 0x2 + ) + + // vfork requires that the child not touch any of the parent's + // active stack frames. Hence, the child does all post-fork + // processing in this stack frame and never returns, while the + // parent returns immediately from this frame and does all + // post-fork processing in the outer frame. + // + // Declare all variables at top in case any + // declarations require heap allocation (e.g., err2). + // ":=" should not be used to declare any variable after + // the call to runtime_BeforeFork. + // + // NOTE(bcmills): The allocation behavior described in the above comment + // seems to lack a corresponding test, and it may be rendered invalid + // by an otherwise-correct change in the compiler. + var ( + err2 Errno + nextfd int + i int + caps caps + fd1, flags uintptr + puid, psetgroups, pgid []byte + uidmap, setgroups, gidmap []byte + clone3 *cloneArgs + pgrp int32 + dirfd int + cred *Credential + ngroups, groups uintptr + c uintptr + ) + + rlim, rlimOK := origRlimitNofile.Load().(Rlimit) + + if sys.UidMappings != nil { + puid = []byte("/proc/self/uid_map\000") + uidmap = formatIDMappings(sys.UidMappings) + } + + if sys.GidMappings != nil { + psetgroups = []byte("/proc/self/setgroups\000") + pgid = []byte("/proc/self/gid_map\000") + + if sys.GidMappingsEnableSetgroups { + setgroups = []byte("allow\000") + } else { + setgroups = []byte("deny\000") + } + gidmap = formatIDMappings(sys.GidMappings) + } + + // Record parent PID so child can test if it has died. + ppid, _ := rawSyscallNoError(SYS_GETPID, 0, 0, 0) + + // Guard against side effects of shuffling fds below. + // Make sure that nextfd is beyond any currently open files so + // that we can't run the risk of overwriting any of them. + fd := make([]int, len(attr.Files)) + nextfd = len(attr.Files) + for i, ufd := range attr.Files { + if nextfd < int(ufd) { + nextfd = int(ufd) + } + fd[i] = int(ufd) + } + nextfd++ + + // Allocate another pipe for parent to child communication for + // synchronizing writing of User ID/Group ID mappings. + if sys.UidMappings != nil || sys.GidMappings != nil { + if err := forkExecPipe(mapPipe[:]); err != nil { + err1 = err.(Errno) + return + } + } + + flags = sys.Cloneflags + if sys.Cloneflags&CLONE_NEWUSER == 0 && sys.Unshareflags&CLONE_NEWUSER == 0 { + flags |= CLONE_VFORK | CLONE_VM + } + // Whether to use clone3. + if sys.UseCgroupFD { + clone3 = &cloneArgs{ + flags: uint64(flags) | CLONE_INTO_CGROUP, + exitSignal: uint64(SIGCHLD), + cgroup: uint64(sys.CgroupFD), + } + } else if flags&CLONE_NEWTIME != 0 { + clone3 = &cloneArgs{ + flags: uint64(flags), + exitSignal: uint64(SIGCHLD), + } + } + + // About to call fork. + // No more allocation or calls of non-assembly functions. + runtime_BeforeFork() + locked = true + if clone3 != nil { + pid, err1 = rawVforkSyscall(_SYS_clone3, uintptr(unsafe.Pointer(clone3)), unsafe.Sizeof(*clone3)) + } else { + flags |= uintptr(SIGCHLD) + if runtime.GOARCH == "s390x" { + // On Linux/s390, the first two arguments of clone(2) are swapped. + pid, err1 = rawVforkSyscall(SYS_CLONE, 0, flags) + } else { + pid, err1 = rawVforkSyscall(SYS_CLONE, flags, 0) + } + } + if err1 != 0 || pid != 0 { + // If we're in the parent, we must return immediately + // so we're not in the same stack frame as the child. + // This can at most use the return PC, which the child + // will not modify, and the results of + // rawVforkSyscall, which must have been written after + // the child was replaced. + return + } + + // Fork succeeded, now in child. + + // Enable the "keep capabilities" flag to set ambient capabilities later. + if len(sys.AmbientCaps) > 0 { + _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_KEEPCAPS, 1, 0, 0, 0, 0) + if err1 != 0 { + goto childerror + } + } + + // Wait for User ID/Group ID mappings to be written. + if sys.UidMappings != nil || sys.GidMappings != nil { + if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(mapPipe[1]), 0, 0); err1 != 0 { + goto childerror + } + pid, _, err1 = RawSyscall(SYS_READ, uintptr(mapPipe[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) + if err1 != 0 { + goto childerror + } + if pid != unsafe.Sizeof(err2) { + err1 = EINVAL + goto childerror + } + if err2 != 0 { + err1 = err2 + goto childerror + } + } + + // Session ID + if sys.Setsid { + _, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0) + if err1 != 0 { + goto childerror + } + } + + // Set process group + if sys.Setpgid || sys.Foreground { + // Place child in process group. + _, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0) + if err1 != 0 { + goto childerror + } + } + + if sys.Foreground { + pgrp = int32(sys.Pgid) + if pgrp == 0 { + pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) + + pgrp = int32(pid) + } + + // Place process group in foreground. + _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp))) + if err1 != 0 { + goto childerror + } + } + + // Restore the signal mask. We do this after TIOCSPGRP to avoid + // having the kernel send a SIGTTOU signal to the process group. + runtime_AfterForkInChild() + + // Unshare + if sys.Unshareflags != 0 { + _, _, err1 = RawSyscall(SYS_UNSHARE, sys.Unshareflags, 0, 0) + if err1 != 0 { + goto childerror + } + + if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.GidMappings != nil { + dirfd = int(_AT_FDCWD) + if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&psetgroups[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { + goto childerror + } + pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&setgroups[0])), uintptr(len(setgroups))) + if err1 != 0 { + goto childerror + } + if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { + goto childerror + } + + if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&pgid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { + goto childerror + } + pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&gidmap[0])), uintptr(len(gidmap))) + if err1 != 0 { + goto childerror + } + if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { + goto childerror + } + } + + if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.UidMappings != nil { + dirfd = int(_AT_FDCWD) + if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&puid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { + goto childerror + } + pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&uidmap[0])), uintptr(len(uidmap))) + if err1 != 0 { + goto childerror + } + if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { + goto childerror + } + } + + // The unshare system call in Linux doesn't unshare mount points + // mounted with --shared. Systemd mounts / with --shared. For a + // long discussion of the pros and cons of this see debian bug 739593. + // The Go model of unsharing is more like Plan 9, where you ask + // to unshare and the namespaces are unconditionally unshared. + // To make this model work we must further mark / as MS_PRIVATE. + // This is what the standard unshare command does. + if sys.Unshareflags&CLONE_NEWNS == CLONE_NEWNS { + _, _, err1 = RawSyscall6(SYS_MOUNT, uintptr(unsafe.Pointer(&none[0])), uintptr(unsafe.Pointer(&slash[0])), 0, MS_REC|MS_PRIVATE, 0, 0) + if err1 != 0 { + goto childerror + } + } + } + + // Chroot + if chroot != nil { + _, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0) + if err1 != 0 { + goto childerror + } + } + + // User and groups + if cred = sys.Credential; cred != nil { + ngroups = uintptr(len(cred.Groups)) + groups = uintptr(0) + if ngroups > 0 { + groups = uintptr(unsafe.Pointer(&cred.Groups[0])) + } + if !(sys.GidMappings != nil && !sys.GidMappingsEnableSetgroups && ngroups == 0) && !cred.NoSetGroups { + _, _, err1 = RawSyscall(_SYS_setgroups, ngroups, groups, 0) + if err1 != 0 { + goto childerror + } + } + _, _, err1 = RawSyscall(sys_SETGID, uintptr(cred.Gid), 0, 0) + if err1 != 0 { + goto childerror + } + _, _, err1 = RawSyscall(sys_SETUID, uintptr(cred.Uid), 0, 0) + if err1 != 0 { + goto childerror + } + } + + if len(sys.AmbientCaps) != 0 { + // Ambient capabilities were added in the 4.3 kernel, + // so it is safe to always use _LINUX_CAPABILITY_VERSION_3. + caps.hdr.version = _LINUX_CAPABILITY_VERSION_3 + + if _, _, err1 = RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { + goto childerror + } + + for _, c = range sys.AmbientCaps { + // Add the c capability to the permitted and inheritable capability mask, + // otherwise we will not be able to add it to the ambient capability mask. + caps.data[capToIndex(c)].permitted |= capToMask(c) + caps.data[capToIndex(c)].inheritable |= capToMask(c) + } + + if _, _, err1 = RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { + goto childerror + } + + for _, c = range sys.AmbientCaps { + _, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0) + if err1 != 0 { + goto childerror + } + } + } + + // Chdir + if dir != nil { + _, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0) + if err1 != 0 { + goto childerror + } + } + + // Parent death signal + if sys.Pdeathsig != 0 { + _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 0, 0, 0) + if err1 != 0 { + goto childerror + } + + // Signal self if parent is already dead. This might cause a + // duplicate signal in rare cases, but it won't matter when + // using SIGKILL. + pid, _ = rawSyscallNoError(SYS_GETPPID, 0, 0, 0) + if pid != ppid { + pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) + _, _, err1 = RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0) + if err1 != 0 { + goto childerror + } + } + } + + // Pass 1: look for fd[i] < i and move those up above len(fd) + // so that pass 2 won't stomp on an fd it needs later. + if pipe < nextfd { + _, _, err1 = RawSyscall(SYS_DUP3, uintptr(pipe), uintptr(nextfd), O_CLOEXEC) + if err1 != 0 { + goto childerror + } + pipe = nextfd + nextfd++ + } + for i = 0; i < len(fd); i++ { + if fd[i] >= 0 && fd[i] < i { + if nextfd == pipe { // don't stomp on pipe + nextfd++ + } + _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC) + if err1 != 0 { + goto childerror + } + fd[i] = nextfd + nextfd++ + } + } + + // Pass 2: dup fd[i] down onto i. + for i = 0; i < len(fd); i++ { + if fd[i] == -1 { + RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) + continue + } + if fd[i] == i { + // dup2(i, i) won't clear close-on-exec flag on Linux, + // probably not elsewhere either. + _, _, err1 = RawSyscall(fcntl64Syscall, uintptr(fd[i]), F_SETFD, 0) + if err1 != 0 { + goto childerror + } + continue + } + // The new fd is created NOT close-on-exec, + // which is exactly what we want. + _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(i), 0) + if err1 != 0 { + goto childerror + } + } + + // By convention, we don't close-on-exec the fds we are + // started with, so if len(fd) < 3, close 0, 1, 2 as needed. + // Programs that know they inherit fds >= 3 will need + // to set them close-on-exec. + for i = len(fd); i < 3; i++ { + RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) + } + + // Detach fd 0 from tty + if sys.Noctty { + _, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0) + if err1 != 0 { + goto childerror + } + } + + // Set the controlling TTY to Ctty + if sys.Setctty { + _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 1) + if err1 != 0 { + goto childerror + } + } + + // Restore original rlimit. + if rlimOK && rlim.Cur != 0 { + rawSetrlimit(RLIMIT_NOFILE, &rlim) + } + + // Enable tracing if requested. + // Do this right before exec so that we don't unnecessarily trace the runtime + // setting up after the fork. See issue #21428. + if sys.Ptrace { + _, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0) + if err1 != 0 { + goto childerror + } + } + + // Time to exec. + _, _, err1 = RawSyscall(SYS_EXECVE, + uintptr(unsafe.Pointer(argv0)), + uintptr(unsafe.Pointer(&argv[0])), + uintptr(unsafe.Pointer(&envv[0]))) + +childerror: + // send error code on pipe + RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1)) + for { + RawSyscall(SYS_EXIT, 253, 0, 0) + } +} + +func formatIDMappings(idMap []SysProcIDMap) []byte { + var data []byte + for _, im := range idMap { + data = append(data, itoa.Itoa(im.ContainerID)+" "+itoa.Itoa(im.HostID)+" "+itoa.Itoa(im.Size)+"\n"...) + } + return data +} + +// writeIDMappings writes the user namespace User ID or Group ID mappings to the specified path. +func writeIDMappings(path string, idMap []SysProcIDMap) error { + fd, err := Open(path, O_RDWR, 0) + if err != nil { + return err + } + + if _, err := Write(fd, formatIDMappings(idMap)); err != nil { + Close(fd) + return err + } + + if err := Close(fd); err != nil { + return err + } + + return nil +} + +// writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false +// and "allow" if enable is true. +// This is needed since kernel 3.19, because you can't write gid_map without +// disabling setgroups() system call. +func writeSetgroups(pid int, enable bool) error { + sgf := "/proc/" + itoa.Itoa(pid) + "/setgroups" + fd, err := Open(sgf, O_RDWR, 0) + if err != nil { + return err + } + + var data []byte + if enable { + data = []byte("allow") + } else { + data = []byte("deny") + } + + if _, err := Write(fd, data); err != nil { + Close(fd) + return err + } + + return Close(fd) +} + +// writeUidGidMappings writes User ID and Group ID mappings for user namespaces +// for a process and it is called from the parent process. +func writeUidGidMappings(pid int, sys *SysProcAttr) error { + if sys.UidMappings != nil { + uidf := "/proc/" + itoa.Itoa(pid) + "/uid_map" + if err := writeIDMappings(uidf, sys.UidMappings); err != nil { + return err + } + } + + if sys.GidMappings != nil { + // If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK. + if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT { + return err + } + gidf := "/proc/" + itoa.Itoa(pid) + "/gid_map" + if err := writeIDMappings(gidf, sys.GidMappings); err != nil { + return err + } + } + + return nil +} |