| // 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). |
| // |
| // Note that User Namespaces are not available on a number of popular Linux |
| // versions (due to security issues), or are available but subject to AppArmor |
| // restrictions like in Ubuntu 24.04. |
| 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. |
| Unshareflags uintptr // Flags for unshare calls. |
| 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. |
| UseCgroupFD bool // Whether to make use of the CgroupFD field. |
| CgroupFD int // File descriptor of a cgroup to put the new process into. |
| // PidFD, if not nil, is used to store the pidfd of a child, if the |
| // functionality is supported by the kernel, or -1. Note *PidFD is |
| // changed only if the process starts successfully. |
| PidFD *int |
| } |
| |
| var ( |
| none = [...]byte{'n', 'o', 'n', 'e', 0} |
| slash = [...]byte{'/', 0} |
| |
| forceClone3 = false // Used by unit tests only. |
| ) |
| |
| // 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, pidfd, 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.PidFD != nil { |
| *sys.PidFD = int(pidfd) |
| } |
| |
| 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, pidfd int32, 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 *Rlimit |
| lim Rlimit |
| ) |
| pidfd = -1 |
| |
| rlim = origRlimitNofile.Load() |
| |
| 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 |
| } |
| if sys.PidFD != nil { |
| flags |= CLONE_PIDFD |
| } |
| // Whether to use clone3. |
| if sys.UseCgroupFD || flags&CLONE_NEWTIME != 0 || forceClone3 { |
| clone3 = &cloneArgs{ |
| flags: uint64(flags), |
| exitSignal: uint64(SIGCHLD), |
| } |
| if sys.UseCgroupFD { |
| clone3.flags |= CLONE_INTO_CGROUP |
| clone3.cgroup = uint64(sys.CgroupFD) |
| } |
| if sys.PidFD != nil { |
| clone3.pidFD = uint64(uintptr(unsafe.Pointer(&pidfd))) |
| } |
| } |
| |
| // 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), 0) |
| } 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, uintptr(unsafe.Pointer(&pidfd))) |
| } else { |
| pid, err1 = rawVforkSyscall(SYS_CLONE, flags, 0, uintptr(unsafe.Pointer(&pidfd))) |
| } |
| } |
| 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, fd1, uintptr(unsafe.Pointer(&setgroups[0])), uintptr(len(setgroups))) |
| if err1 != 0 { |
| goto childerror |
| } |
| if _, _, err1 = RawSyscall(SYS_CLOSE, 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, fd1, uintptr(unsafe.Pointer(&gidmap[0])), uintptr(len(gidmap))) |
| if err1 != 0 { |
| goto childerror |
| } |
| if _, _, err1 = RawSyscall(SYS_CLOSE, 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, fd1, uintptr(unsafe.Pointer(&uidmap[0])), uintptr(len(uidmap))) |
| if err1 != 0 { |
| goto childerror |
| } |
| if _, _, err1 = RawSyscall(SYS_CLOSE, 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 rlim != nil { |
| // Some other process may have changed our rlimit by |
| // calling prlimit. We can check for that case because |
| // our current rlimit will not be the value we set when |
| // caching the rlimit in the init function in rlimit.go. |
| // |
| // Note that this test is imperfect, since it won't catch |
| // the case in which some other process used prlimit to |
| // set our rlimits to max-1/max. In that case we will fall |
| // back to the original cur/max when starting the child. |
| // We hope that setting to max-1/max is unlikely. |
| _, _, err1 = RawSyscall6(SYS_PRLIMIT64, 0, RLIMIT_NOFILE, 0, uintptr(unsafe.Pointer(&lim)), 0, 0) |
| if err1 != 0 || (lim.Cur == rlim.Max-1 && lim.Max == rlim.Max) { |
| RawSyscall6(SYS_PRLIMIT64, 0, RLIMIT_NOFILE, uintptr(unsafe.Pointer(rlim)), 0, 0, 0) |
| } |
| } |
| |
| // 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 |
| } |
| |
| // forkAndExecFailureCleanup cleans up after an exec failure. |
| func forkAndExecFailureCleanup(attr *ProcAttr, sys *SysProcAttr) { |
| if sys.PidFD != nil && *sys.PidFD != -1 { |
| Close(*sys.PidFD) |
| *sys.PidFD = -1 |
| } |
| } |