diff options
Diffstat (limited to 'src/syscall/exec_linux.go')
| -rw-r--r-- | src/syscall/exec_linux.go | 648 |
1 files changed, 648 insertions, 0 deletions
diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go new file mode 100644 index 0000000..b6acad9 --- /dev/null +++ b/src/syscall/exec_linux.go @@ -0,0 +1,648 @@ +// 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. + +// +build linux + +package syscall + +import ( + "runtime" + "unsafe" +) + +// 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 Signal // Signal that the process will get when its parent dies (Linux only) + 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) +} + +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. + r1, err1, p, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe) + if locked { + runtime_AfterFork() + } + if err1 != 0 { + return 0, err1 + } + + // parent; return PID + pid = int(r1) + + if sys.UidMappings != nil || sys.GidMappings != nil { + Close(p[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(p[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) + Close(p[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) } + +// 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 +func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (r1 uintptr, err1 Errno, p [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., err1). + var ( + err2 Errno + nextfd int + i int + caps caps + fd1 uintptr + puid, psetgroups, pgid []byte + uidmap, setgroups, gidmap []byte + ) + + 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(p[:]); err != nil { + err1 = err.(Errno) + return + } + } + + var hasRawVforkSyscall bool + switch runtime.GOARCH { + case "amd64", "arm64", "ppc64", "riscv64", "s390x": + hasRawVforkSyscall = true + } + + // About to call fork. + // No more allocation or calls of non-assembly functions. + runtime_BeforeFork() + locked = true + switch { + case hasRawVforkSyscall && (sys.Cloneflags&CLONE_NEWUSER == 0 && sys.Unshareflags&CLONE_NEWUSER == 0): + r1, err1 = rawVforkSyscall(SYS_CLONE, uintptr(SIGCHLD|CLONE_VFORK|CLONE_VM)|sys.Cloneflags) + case runtime.GOARCH == "s390x": + r1, _, err1 = RawSyscall6(SYS_CLONE, 0, uintptr(SIGCHLD)|sys.Cloneflags, 0, 0, 0, 0) + default: + r1, _, err1 = RawSyscall6(SYS_CLONE, uintptr(SIGCHLD)|sys.Cloneflags, 0, 0, 0, 0, 0) + } + if err1 != 0 || r1 != 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. + + runtime_AfterForkInChild() + + // 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(p[1]), 0, 0); err1 != 0 { + goto childerror + } + r1, _, err1 = RawSyscall(SYS_READ, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) + if err1 != 0 { + goto childerror + } + if r1 != 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 { + r1, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) + + pgrp = int32(r1) + } + + // Place process group in foreground. + _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp))) + if err1 != 0 { + goto childerror + } + } + + // 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 + } + r1, _, 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 + } + r1, _, 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 + } + r1, _, 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. + r1, _ = rawSyscallNoError(SYS_GETPPID, 0, 0, 0) + if r1 != 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 _SYS_dup != SYS_DUP3 && err1 == ENOSYS { + _, _, err1 = RawSyscall(_SYS_dup, uintptr(pipe), uintptr(nextfd), 0) + if err1 != 0 { + goto childerror + } + RawSyscall(fcntl64Syscall, uintptr(nextfd), F_SETFD, FD_CLOEXEC) + } else if err1 != 0 { + goto childerror + } + pipe = nextfd + nextfd++ + } + for i = 0; i < len(fd); i++ { + if fd[i] >= 0 && fd[i] < int(i) { + if nextfd == pipe { // don't stomp on pipe + nextfd++ + } + _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC) + if _SYS_dup != SYS_DUP3 && err1 == ENOSYS { + _, _, err1 = RawSyscall(_SYS_dup, uintptr(fd[i]), uintptr(nextfd), 0) + if err1 != 0 { + goto childerror + } + RawSyscall(fcntl64Syscall, uintptr(nextfd), F_SETFD, FD_CLOEXEC) + } else 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] == int(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_dup, 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 + } + } + + // 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) + } +} + +// Try to open a pipe with O_CLOEXEC set on both file descriptors. +func forkExecPipe(p []int) (err error) { + err = Pipe2(p, O_CLOEXEC) + // pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it + // might not be implemented. + if err == ENOSYS { + if err = Pipe(p); err != nil { + return + } + if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil { + return + } + _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC) + } + return +} + +func formatIDMappings(idMap []SysProcIDMap) []byte { + var data []byte + for _, im := range idMap { + data = append(data, []byte(itoa(im.ContainerID)+" "+itoa(im.HostID)+" "+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(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(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(pid) + "/gid_map" + if err := writeIDMappings(gidf, sys.GidMappings); err != nil { + return err + } + } + + return nil +} |