1// Copyright 2011 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5//go:build linux 6 7package syscall 8 9import ( 10 "internal/itoa" 11 "runtime" 12 "unsafe" 13) 14 15// Linux unshare/clone/clone2/clone3 flags, architecture-independent, 16// copied from linux/sched.h. 17const ( 18 CLONE_VM = 0x00000100 // set if VM shared between processes 19 CLONE_FS = 0x00000200 // set if fs info shared between processes 20 CLONE_FILES = 0x00000400 // set if open files shared between processes 21 CLONE_SIGHAND = 0x00000800 // set if signal handlers and blocked signals shared 22 CLONE_PIDFD = 0x00001000 // set if a pidfd should be placed in parent 23 CLONE_PTRACE = 0x00002000 // set if we want to let tracing continue on the child too 24 CLONE_VFORK = 0x00004000 // set if the parent wants the child to wake it up on mm_release 25 CLONE_PARENT = 0x00008000 // set if we want to have the same parent as the cloner 26 CLONE_THREAD = 0x00010000 // Same thread group? 27 CLONE_NEWNS = 0x00020000 // New mount namespace group 28 CLONE_SYSVSEM = 0x00040000 // share system V SEM_UNDO semantics 29 CLONE_SETTLS = 0x00080000 // create a new TLS for the child 30 CLONE_PARENT_SETTID = 0x00100000 // set the TID in the parent 31 CLONE_CHILD_CLEARTID = 0x00200000 // clear the TID in the child 32 CLONE_DETACHED = 0x00400000 // Unused, ignored 33 CLONE_UNTRACED = 0x00800000 // set if the tracing process can't force CLONE_PTRACE on this clone 34 CLONE_CHILD_SETTID = 0x01000000 // set the TID in the child 35 CLONE_NEWCGROUP = 0x02000000 // New cgroup namespace 36 CLONE_NEWUTS = 0x04000000 // New utsname namespace 37 CLONE_NEWIPC = 0x08000000 // New ipc namespace 38 CLONE_NEWUSER = 0x10000000 // New user namespace 39 CLONE_NEWPID = 0x20000000 // New pid namespace 40 CLONE_NEWNET = 0x40000000 // New network namespace 41 CLONE_IO = 0x80000000 // Clone io context 42 43 // Flags for the clone3() syscall. 44 45 CLONE_CLEAR_SIGHAND = 0x100000000 // Clear any signal handler and reset to SIG_DFL. 46 CLONE_INTO_CGROUP = 0x200000000 // Clone into a specific cgroup given the right permissions. 47 48 // Cloning flags intersect with CSIGNAL so can be used with unshare and clone3 49 // syscalls only: 50 51 CLONE_NEWTIME = 0x00000080 // New time namespace 52) 53 54// SysProcIDMap holds Container ID to Host ID mappings used for User Namespaces in Linux. 55// See user_namespaces(7). 56// 57// Note that User Namespaces are not available on a number of popular Linux 58// versions (due to security issues), or are available but subject to AppArmor 59// restrictions like in Ubuntu 24.04. 60type SysProcIDMap struct { 61 ContainerID int // Container ID. 62 HostID int // Host ID. 63 Size int // Size. 64} 65 66type SysProcAttr struct { 67 Chroot string // Chroot. 68 Credential *Credential // Credential. 69 // Ptrace tells the child to call ptrace(PTRACE_TRACEME). 70 // Call runtime.LockOSThread before starting a process with this set, 71 // and don't call UnlockOSThread until done with PtraceSyscall calls. 72 Ptrace bool 73 Setsid bool // Create session. 74 // Setpgid sets the process group ID of the child to Pgid, 75 // or, if Pgid == 0, to the new child's process ID. 76 Setpgid bool 77 // Setctty sets the controlling terminal of the child to 78 // file descriptor Ctty. Ctty must be a descriptor number 79 // in the child process: an index into ProcAttr.Files. 80 // This is only meaningful if Setsid is true. 81 Setctty bool 82 Noctty bool // Detach fd 0 from controlling terminal. 83 Ctty int // Controlling TTY fd. 84 // Foreground places the child process group in the foreground. 85 // This implies Setpgid. The Ctty field must be set to 86 // the descriptor of the controlling TTY. 87 // Unlike Setctty, in this case Ctty must be a descriptor 88 // number in the parent process. 89 Foreground bool 90 Pgid int // Child's process group ID if Setpgid. 91 // Pdeathsig, if non-zero, is a signal that the kernel will send to 92 // the child process when the creating thread dies. Note that the signal 93 // is sent on thread termination, which may happen before process termination. 94 // There are more details at https://go.dev/issue/27505. 95 Pdeathsig Signal 96 Cloneflags uintptr // Flags for clone calls. 97 Unshareflags uintptr // Flags for unshare calls. 98 UidMappings []SysProcIDMap // User ID mappings for user namespaces. 99 GidMappings []SysProcIDMap // Group ID mappings for user namespaces. 100 // GidMappingsEnableSetgroups enabling setgroups syscall. 101 // If false, then setgroups syscall will be disabled for the child process. 102 // This parameter is no-op if GidMappings == nil. Otherwise for unprivileged 103 // users this should be set to false for mappings work. 104 GidMappingsEnableSetgroups bool 105 AmbientCaps []uintptr // Ambient capabilities. 106 UseCgroupFD bool // Whether to make use of the CgroupFD field. 107 CgroupFD int // File descriptor of a cgroup to put the new process into. 108 // PidFD, if not nil, is used to store the pidfd of a child, if the 109 // functionality is supported by the kernel, or -1. Note *PidFD is 110 // changed only if the process starts successfully. 111 PidFD *int 112} 113 114var ( 115 none = [...]byte{'n', 'o', 'n', 'e', 0} 116 slash = [...]byte{'/', 0} 117 118 forceClone3 = false // Used by unit tests only. 119) 120 121// Implemented in runtime package. 122func runtime_BeforeFork() 123func runtime_AfterFork() 124func runtime_AfterForkInChild() 125 126// Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child. 127// If a dup or exec fails, write the errno error to pipe. 128// (Pipe is close-on-exec so if exec succeeds, it will be closed.) 129// In the child, this function must not acquire any locks, because 130// they might have been locked at the time of the fork. This means 131// no rescheduling, no malloc calls, and no new stack segments. 132// For the same reason compiler does not race instrument it. 133// The calls to RawSyscall are okay because they are assembly 134// functions that do not grow the stack. 135// 136//go:norace 137func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) { 138 // Set up and fork. This returns immediately in the parent or 139 // if there's an error. 140 upid, pidfd, err, mapPipe, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe) 141 if locked { 142 runtime_AfterFork() 143 } 144 if err != 0 { 145 return 0, err 146 } 147 148 // parent; return PID 149 pid = int(upid) 150 if sys.PidFD != nil { 151 *sys.PidFD = int(pidfd) 152 } 153 154 if sys.UidMappings != nil || sys.GidMappings != nil { 155 Close(mapPipe[0]) 156 var err2 Errno 157 // uid/gid mappings will be written after fork and unshare(2) for user 158 // namespaces. 159 if sys.Unshareflags&CLONE_NEWUSER == 0 { 160 if err := writeUidGidMappings(pid, sys); err != nil { 161 err2 = err.(Errno) 162 } 163 } 164 RawSyscall(SYS_WRITE, uintptr(mapPipe[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) 165 Close(mapPipe[1]) 166 } 167 168 return pid, 0 169} 170 171const _LINUX_CAPABILITY_VERSION_3 = 0x20080522 172 173type capHeader struct { 174 version uint32 175 pid int32 176} 177 178type capData struct { 179 effective uint32 180 permitted uint32 181 inheritable uint32 182} 183type caps struct { 184 hdr capHeader 185 data [2]capData 186} 187 188// See CAP_TO_INDEX in linux/capability.h: 189func capToIndex(cap uintptr) uintptr { return cap >> 5 } 190 191// See CAP_TO_MASK in linux/capability.h: 192func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) } 193 194// cloneArgs holds arguments for clone3 Linux syscall. 195type cloneArgs struct { 196 flags uint64 // Flags bit mask 197 pidFD uint64 // Where to store PID file descriptor (int *) 198 childTID uint64 // Where to store child TID, in child's memory (pid_t *) 199 parentTID uint64 // Where to store child TID, in parent's memory (pid_t *) 200 exitSignal uint64 // Signal to deliver to parent on child termination 201 stack uint64 // Pointer to lowest byte of stack 202 stackSize uint64 // Size of stack 203 tls uint64 // Location of new TLS 204 setTID uint64 // Pointer to a pid_t array (since Linux 5.5) 205 setTIDSize uint64 // Number of elements in set_tid (since Linux 5.5) 206 cgroup uint64 // File descriptor for target cgroup of child (since Linux 5.7) 207} 208 209// forkAndExecInChild1 implements the body of forkAndExecInChild up to 210// the parent's post-fork path. This is a separate function so we can 211// separate the child's and parent's stack frames if we're using 212// vfork. 213// 214// This is go:noinline because the point is to keep the stack frames 215// of this and forkAndExecInChild separate. 216// 217//go:noinline 218//go:norace 219//go:nocheckptr 220func 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) { 221 // Defined in linux/prctl.h starting with Linux 4.3. 222 const ( 223 PR_CAP_AMBIENT = 0x2f 224 PR_CAP_AMBIENT_RAISE = 0x2 225 ) 226 227 // vfork requires that the child not touch any of the parent's 228 // active stack frames. Hence, the child does all post-fork 229 // processing in this stack frame and never returns, while the 230 // parent returns immediately from this frame and does all 231 // post-fork processing in the outer frame. 232 // 233 // Declare all variables at top in case any 234 // declarations require heap allocation (e.g., err2). 235 // ":=" should not be used to declare any variable after 236 // the call to runtime_BeforeFork. 237 // 238 // NOTE(bcmills): The allocation behavior described in the above comment 239 // seems to lack a corresponding test, and it may be rendered invalid 240 // by an otherwise-correct change in the compiler. 241 var ( 242 err2 Errno 243 nextfd int 244 i int 245 caps caps 246 fd1, flags uintptr 247 puid, psetgroups, pgid []byte 248 uidmap, setgroups, gidmap []byte 249 clone3 *cloneArgs 250 pgrp int32 251 dirfd int 252 cred *Credential 253 ngroups, groups uintptr 254 c uintptr 255 ) 256 pidfd = -1 257 258 rlim := origRlimitNofile.Load() 259 260 if sys.UidMappings != nil { 261 puid = []byte("/proc/self/uid_map\000") 262 uidmap = formatIDMappings(sys.UidMappings) 263 } 264 265 if sys.GidMappings != nil { 266 psetgroups = []byte("/proc/self/setgroups\000") 267 pgid = []byte("/proc/self/gid_map\000") 268 269 if sys.GidMappingsEnableSetgroups { 270 setgroups = []byte("allow\000") 271 } else { 272 setgroups = []byte("deny\000") 273 } 274 gidmap = formatIDMappings(sys.GidMappings) 275 } 276 277 // Record parent PID so child can test if it has died. 278 ppid, _ := rawSyscallNoError(SYS_GETPID, 0, 0, 0) 279 280 // Guard against side effects of shuffling fds below. 281 // Make sure that nextfd is beyond any currently open files so 282 // that we can't run the risk of overwriting any of them. 283 fd := make([]int, len(attr.Files)) 284 nextfd = len(attr.Files) 285 for i, ufd := range attr.Files { 286 if nextfd < int(ufd) { 287 nextfd = int(ufd) 288 } 289 fd[i] = int(ufd) 290 } 291 nextfd++ 292 293 // Allocate another pipe for parent to child communication for 294 // synchronizing writing of User ID/Group ID mappings. 295 if sys.UidMappings != nil || sys.GidMappings != nil { 296 if err := forkExecPipe(mapPipe[:]); err != nil { 297 err1 = err.(Errno) 298 return 299 } 300 } 301 302 flags = sys.Cloneflags 303 if sys.Cloneflags&CLONE_NEWUSER == 0 && sys.Unshareflags&CLONE_NEWUSER == 0 { 304 flags |= CLONE_VFORK | CLONE_VM 305 } 306 if sys.PidFD != nil { 307 flags |= CLONE_PIDFD 308 } 309 // Whether to use clone3. 310 if sys.UseCgroupFD || flags&CLONE_NEWTIME != 0 || forceClone3 { 311 clone3 = &cloneArgs{ 312 flags: uint64(flags), 313 exitSignal: uint64(SIGCHLD), 314 } 315 if sys.UseCgroupFD { 316 clone3.flags |= CLONE_INTO_CGROUP 317 clone3.cgroup = uint64(sys.CgroupFD) 318 } 319 if sys.PidFD != nil { 320 clone3.pidFD = uint64(uintptr(unsafe.Pointer(&pidfd))) 321 } 322 } 323 324 // About to call fork. 325 // No more allocation or calls of non-assembly functions. 326 runtime_BeforeFork() 327 locked = true 328 if clone3 != nil { 329 pid, err1 = rawVforkSyscall(_SYS_clone3, uintptr(unsafe.Pointer(clone3)), unsafe.Sizeof(*clone3), 0) 330 } else { 331 flags |= uintptr(SIGCHLD) 332 if runtime.GOARCH == "s390x" { 333 // On Linux/s390, the first two arguments of clone(2) are swapped. 334 pid, err1 = rawVforkSyscall(SYS_CLONE, 0, flags, uintptr(unsafe.Pointer(&pidfd))) 335 } else { 336 pid, err1 = rawVforkSyscall(SYS_CLONE, flags, 0, uintptr(unsafe.Pointer(&pidfd))) 337 } 338 } 339 if err1 != 0 || pid != 0 { 340 // If we're in the parent, we must return immediately 341 // so we're not in the same stack frame as the child. 342 // This can at most use the return PC, which the child 343 // will not modify, and the results of 344 // rawVforkSyscall, which must have been written after 345 // the child was replaced. 346 return 347 } 348 349 // Fork succeeded, now in child. 350 351 // Enable the "keep capabilities" flag to set ambient capabilities later. 352 if len(sys.AmbientCaps) > 0 { 353 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_KEEPCAPS, 1, 0, 0, 0, 0) 354 if err1 != 0 { 355 goto childerror 356 } 357 } 358 359 // Wait for User ID/Group ID mappings to be written. 360 if sys.UidMappings != nil || sys.GidMappings != nil { 361 if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(mapPipe[1]), 0, 0); err1 != 0 { 362 goto childerror 363 } 364 pid, _, err1 = RawSyscall(SYS_READ, uintptr(mapPipe[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) 365 if err1 != 0 { 366 goto childerror 367 } 368 if pid != unsafe.Sizeof(err2) { 369 err1 = EINVAL 370 goto childerror 371 } 372 if err2 != 0 { 373 err1 = err2 374 goto childerror 375 } 376 } 377 378 // Session ID 379 if sys.Setsid { 380 _, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0) 381 if err1 != 0 { 382 goto childerror 383 } 384 } 385 386 // Set process group 387 if sys.Setpgid || sys.Foreground { 388 // Place child in process group. 389 _, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0) 390 if err1 != 0 { 391 goto childerror 392 } 393 } 394 395 if sys.Foreground { 396 pgrp = int32(sys.Pgid) 397 if pgrp == 0 { 398 pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) 399 400 pgrp = int32(pid) 401 } 402 403 // Place process group in foreground. 404 _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp))) 405 if err1 != 0 { 406 goto childerror 407 } 408 } 409 410 // Restore the signal mask. We do this after TIOCSPGRP to avoid 411 // having the kernel send a SIGTTOU signal to the process group. 412 runtime_AfterForkInChild() 413 414 // Unshare 415 if sys.Unshareflags != 0 { 416 _, _, err1 = RawSyscall(SYS_UNSHARE, sys.Unshareflags, 0, 0) 417 if err1 != 0 { 418 goto childerror 419 } 420 421 if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.GidMappings != nil { 422 dirfd = int(_AT_FDCWD) 423 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&psetgroups[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 424 goto childerror 425 } 426 pid, _, err1 = RawSyscall(SYS_WRITE, fd1, uintptr(unsafe.Pointer(&setgroups[0])), uintptr(len(setgroups))) 427 if err1 != 0 { 428 goto childerror 429 } 430 if _, _, err1 = RawSyscall(SYS_CLOSE, fd1, 0, 0); err1 != 0 { 431 goto childerror 432 } 433 434 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&pgid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 435 goto childerror 436 } 437 pid, _, err1 = RawSyscall(SYS_WRITE, fd1, uintptr(unsafe.Pointer(&gidmap[0])), uintptr(len(gidmap))) 438 if err1 != 0 { 439 goto childerror 440 } 441 if _, _, err1 = RawSyscall(SYS_CLOSE, fd1, 0, 0); err1 != 0 { 442 goto childerror 443 } 444 } 445 446 if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.UidMappings != nil { 447 dirfd = int(_AT_FDCWD) 448 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&puid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 449 goto childerror 450 } 451 pid, _, err1 = RawSyscall(SYS_WRITE, fd1, uintptr(unsafe.Pointer(&uidmap[0])), uintptr(len(uidmap))) 452 if err1 != 0 { 453 goto childerror 454 } 455 if _, _, err1 = RawSyscall(SYS_CLOSE, fd1, 0, 0); err1 != 0 { 456 goto childerror 457 } 458 } 459 460 // The unshare system call in Linux doesn't unshare mount points 461 // mounted with --shared. Systemd mounts / with --shared. For a 462 // long discussion of the pros and cons of this see debian bug 739593. 463 // The Go model of unsharing is more like Plan 9, where you ask 464 // to unshare and the namespaces are unconditionally unshared. 465 // To make this model work we must further mark / as MS_PRIVATE. 466 // This is what the standard unshare command does. 467 if sys.Unshareflags&CLONE_NEWNS == CLONE_NEWNS { 468 _, _, err1 = RawSyscall6(SYS_MOUNT, uintptr(unsafe.Pointer(&none[0])), uintptr(unsafe.Pointer(&slash[0])), 0, MS_REC|MS_PRIVATE, 0, 0) 469 if err1 != 0 { 470 goto childerror 471 } 472 } 473 } 474 475 // Chroot 476 if chroot != nil { 477 _, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0) 478 if err1 != 0 { 479 goto childerror 480 } 481 } 482 483 // User and groups 484 if cred = sys.Credential; cred != nil { 485 ngroups = uintptr(len(cred.Groups)) 486 groups = uintptr(0) 487 if ngroups > 0 { 488 groups = uintptr(unsafe.Pointer(&cred.Groups[0])) 489 } 490 if !(sys.GidMappings != nil && !sys.GidMappingsEnableSetgroups && ngroups == 0) && !cred.NoSetGroups { 491 _, _, err1 = RawSyscall(_SYS_setgroups, ngroups, groups, 0) 492 if err1 != 0 { 493 goto childerror 494 } 495 } 496 _, _, err1 = RawSyscall(sys_SETGID, uintptr(cred.Gid), 0, 0) 497 if err1 != 0 { 498 goto childerror 499 } 500 _, _, err1 = RawSyscall(sys_SETUID, uintptr(cred.Uid), 0, 0) 501 if err1 != 0 { 502 goto childerror 503 } 504 } 505 506 if len(sys.AmbientCaps) != 0 { 507 // Ambient capabilities were added in the 4.3 kernel, 508 // so it is safe to always use _LINUX_CAPABILITY_VERSION_3. 509 caps.hdr.version = _LINUX_CAPABILITY_VERSION_3 510 511 if _, _, err1 = RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { 512 goto childerror 513 } 514 515 for _, c = range sys.AmbientCaps { 516 // Add the c capability to the permitted and inheritable capability mask, 517 // otherwise we will not be able to add it to the ambient capability mask. 518 caps.data[capToIndex(c)].permitted |= capToMask(c) 519 caps.data[capToIndex(c)].inheritable |= capToMask(c) 520 } 521 522 if _, _, err1 = RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { 523 goto childerror 524 } 525 526 for _, c = range sys.AmbientCaps { 527 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0) 528 if err1 != 0 { 529 goto childerror 530 } 531 } 532 } 533 534 // Chdir 535 if dir != nil { 536 _, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0) 537 if err1 != 0 { 538 goto childerror 539 } 540 } 541 542 // Parent death signal 543 if sys.Pdeathsig != 0 { 544 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 0, 0, 0) 545 if err1 != 0 { 546 goto childerror 547 } 548 549 // Signal self if parent is already dead. This might cause a 550 // duplicate signal in rare cases, but it won't matter when 551 // using SIGKILL. 552 pid, _ = rawSyscallNoError(SYS_GETPPID, 0, 0, 0) 553 if pid != ppid { 554 pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) 555 _, _, err1 = RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0) 556 if err1 != 0 { 557 goto childerror 558 } 559 } 560 } 561 562 // Pass 1: look for fd[i] < i and move those up above len(fd) 563 // so that pass 2 won't stomp on an fd it needs later. 564 if pipe < nextfd { 565 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(pipe), uintptr(nextfd), O_CLOEXEC) 566 if err1 != 0 { 567 goto childerror 568 } 569 pipe = nextfd 570 nextfd++ 571 } 572 for i = 0; i < len(fd); i++ { 573 if fd[i] >= 0 && fd[i] < i { 574 if nextfd == pipe { // don't stomp on pipe 575 nextfd++ 576 } 577 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC) 578 if err1 != 0 { 579 goto childerror 580 } 581 fd[i] = nextfd 582 nextfd++ 583 } 584 } 585 586 // Pass 2: dup fd[i] down onto i. 587 for i = 0; i < len(fd); i++ { 588 if fd[i] == -1 { 589 RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) 590 continue 591 } 592 if fd[i] == i { 593 // dup2(i, i) won't clear close-on-exec flag on Linux, 594 // probably not elsewhere either. 595 _, _, err1 = RawSyscall(fcntl64Syscall, uintptr(fd[i]), F_SETFD, 0) 596 if err1 != 0 { 597 goto childerror 598 } 599 continue 600 } 601 // The new fd is created NOT close-on-exec, 602 // which is exactly what we want. 603 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(i), 0) 604 if err1 != 0 { 605 goto childerror 606 } 607 } 608 609 // By convention, we don't close-on-exec the fds we are 610 // started with, so if len(fd) < 3, close 0, 1, 2 as needed. 611 // Programs that know they inherit fds >= 3 will need 612 // to set them close-on-exec. 613 for i = len(fd); i < 3; i++ { 614 RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) 615 } 616 617 // Detach fd 0 from tty 618 if sys.Noctty { 619 _, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0) 620 if err1 != 0 { 621 goto childerror 622 } 623 } 624 625 // Set the controlling TTY to Ctty 626 if sys.Setctty { 627 _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 1) 628 if err1 != 0 { 629 goto childerror 630 } 631 } 632 633 // Restore original rlimit. 634 if rlim != nil { 635 rawSetrlimit(RLIMIT_NOFILE, rlim) 636 } 637 638 // Enable tracing if requested. 639 // Do this right before exec so that we don't unnecessarily trace the runtime 640 // setting up after the fork. See issue #21428. 641 if sys.Ptrace { 642 _, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0) 643 if err1 != 0 { 644 goto childerror 645 } 646 } 647 648 // Time to exec. 649 _, _, err1 = RawSyscall(SYS_EXECVE, 650 uintptr(unsafe.Pointer(argv0)), 651 uintptr(unsafe.Pointer(&argv[0])), 652 uintptr(unsafe.Pointer(&envv[0]))) 653 654childerror: 655 // send error code on pipe 656 RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1)) 657 for { 658 RawSyscall(SYS_EXIT, 253, 0, 0) 659 } 660} 661 662func formatIDMappings(idMap []SysProcIDMap) []byte { 663 var data []byte 664 for _, im := range idMap { 665 data = append(data, itoa.Itoa(im.ContainerID)+" "+itoa.Itoa(im.HostID)+" "+itoa.Itoa(im.Size)+"\n"...) 666 } 667 return data 668} 669 670// writeIDMappings writes the user namespace User ID or Group ID mappings to the specified path. 671func writeIDMappings(path string, idMap []SysProcIDMap) error { 672 fd, err := Open(path, O_RDWR, 0) 673 if err != nil { 674 return err 675 } 676 677 if _, err := Write(fd, formatIDMappings(idMap)); err != nil { 678 Close(fd) 679 return err 680 } 681 682 if err := Close(fd); err != nil { 683 return err 684 } 685 686 return nil 687} 688 689// writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false 690// and "allow" if enable is true. 691// This is needed since kernel 3.19, because you can't write gid_map without 692// disabling setgroups() system call. 693func writeSetgroups(pid int, enable bool) error { 694 sgf := "/proc/" + itoa.Itoa(pid) + "/setgroups" 695 fd, err := Open(sgf, O_RDWR, 0) 696 if err != nil { 697 return err 698 } 699 700 var data []byte 701 if enable { 702 data = []byte("allow") 703 } else { 704 data = []byte("deny") 705 } 706 707 if _, err := Write(fd, data); err != nil { 708 Close(fd) 709 return err 710 } 711 712 return Close(fd) 713} 714 715// writeUidGidMappings writes User ID and Group ID mappings for user namespaces 716// for a process and it is called from the parent process. 717func writeUidGidMappings(pid int, sys *SysProcAttr) error { 718 if sys.UidMappings != nil { 719 uidf := "/proc/" + itoa.Itoa(pid) + "/uid_map" 720 if err := writeIDMappings(uidf, sys.UidMappings); err != nil { 721 return err 722 } 723 } 724 725 if sys.GidMappings != nil { 726 // If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK. 727 if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT { 728 return err 729 } 730 gidf := "/proc/" + itoa.Itoa(pid) + "/gid_map" 731 if err := writeIDMappings(gidf, sys.GidMappings); err != nil { 732 return err 733 } 734 } 735 736 return nil 737} 738 739// forkAndExecFailureCleanup cleans up after an exec failure. 740func forkAndExecFailureCleanup(attr *ProcAttr, sys *SysProcAttr) { 741 if sys.PidFD != nil && *sys.PidFD != -1 { 742 Close(*sys.PidFD) 743 *sys.PidFD = -1 744 } 745} 746