github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/syscall/exec_linux.go (about) 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 7 package syscall 8 9 import ( 10 "internal/itoa" 11 "runtime" 12 "unsafe" 13 ) 14 15 // Linux unshare/clone/clone2/clone3 flags, architecture-independent, 16 // copied from linux/sched.h. 17 const ( 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 type SysProcIDMap struct { 57 ContainerID int // Container ID. 58 HostID int // Host ID. 59 Size int // Size. 60 } 61 62 type SysProcAttr struct { 63 Chroot string // Chroot. 64 Credential *Credential // Credential. 65 // Ptrace tells the child to call ptrace(PTRACE_TRACEME). 66 // Call runtime.LockOSThread before starting a process with this set, 67 // and don't call UnlockOSThread until done with PtraceSyscall calls. 68 Ptrace bool 69 Setsid bool // Create session. 70 // Setpgid sets the process group ID of the child to Pgid, 71 // or, if Pgid == 0, to the new child's process ID. 72 Setpgid bool 73 // Setctty sets the controlling terminal of the child to 74 // file descriptor Ctty. Ctty must be a descriptor number 75 // in the child process: an index into ProcAttr.Files. 76 // This is only meaningful if Setsid is true. 77 Setctty bool 78 Noctty bool // Detach fd 0 from controlling terminal 79 Ctty int // Controlling TTY fd 80 // Foreground places the child process group in the foreground. 81 // This implies Setpgid. The Ctty field must be set to 82 // the descriptor of the controlling TTY. 83 // Unlike Setctty, in this case Ctty must be a descriptor 84 // number in the parent process. 85 Foreground bool 86 Pgid int // Child's process group ID if Setpgid. 87 // Pdeathsig, if non-zero, is a signal that the kernel will send to 88 // the child process when the creating thread dies. Note that the signal 89 // is sent on thread termination, which may happen before process termination. 90 // There are more details at https://go.dev/issue/27505. 91 Pdeathsig Signal 92 Cloneflags uintptr // Flags for clone calls (Linux only) 93 Unshareflags uintptr // Flags for unshare calls (Linux only) 94 UidMappings []SysProcIDMap // User ID mappings for user namespaces. 95 GidMappings []SysProcIDMap // Group ID mappings for user namespaces. 96 // GidMappingsEnableSetgroups enabling setgroups syscall. 97 // If false, then setgroups syscall will be disabled for the child process. 98 // This parameter is no-op if GidMappings == nil. Otherwise for unprivileged 99 // users this should be set to false for mappings work. 100 GidMappingsEnableSetgroups bool 101 AmbientCaps []uintptr // Ambient capabilities (Linux only) 102 UseCgroupFD bool // Whether to make use of the CgroupFD field. 103 CgroupFD int // File descriptor of a cgroup to put the new process into. 104 } 105 106 var ( 107 none = [...]byte{'n', 'o', 'n', 'e', 0} 108 slash = [...]byte{'/', 0} 109 ) 110 111 // Implemented in runtime package. 112 func runtime_BeforeFork() 113 func runtime_AfterFork() 114 func runtime_AfterForkInChild() 115 116 // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child. 117 // If a dup or exec fails, write the errno error to pipe. 118 // (Pipe is close-on-exec so if exec succeeds, it will be closed.) 119 // In the child, this function must not acquire any locks, because 120 // they might have been locked at the time of the fork. This means 121 // no rescheduling, no malloc calls, and no new stack segments. 122 // For the same reason compiler does not race instrument it. 123 // The calls to RawSyscall are okay because they are assembly 124 // functions that do not grow the stack. 125 // 126 //go:norace 127 func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) { 128 // Set up and fork. This returns immediately in the parent or 129 // if there's an error. 130 upid, err, mapPipe, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe) 131 if locked { 132 runtime_AfterFork() 133 } 134 if err != 0 { 135 return 0, err 136 } 137 138 // parent; return PID 139 pid = int(upid) 140 141 if sys.UidMappings != nil || sys.GidMappings != nil { 142 Close(mapPipe[0]) 143 var err2 Errno 144 // uid/gid mappings will be written after fork and unshare(2) for user 145 // namespaces. 146 if sys.Unshareflags&CLONE_NEWUSER == 0 { 147 if err := writeUidGidMappings(pid, sys); err != nil { 148 err2 = err.(Errno) 149 } 150 } 151 RawSyscall(SYS_WRITE, uintptr(mapPipe[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) 152 Close(mapPipe[1]) 153 } 154 155 return pid, 0 156 } 157 158 const _LINUX_CAPABILITY_VERSION_3 = 0x20080522 159 160 type capHeader struct { 161 version uint32 162 pid int32 163 } 164 165 type capData struct { 166 effective uint32 167 permitted uint32 168 inheritable uint32 169 } 170 type caps struct { 171 hdr capHeader 172 data [2]capData 173 } 174 175 // See CAP_TO_INDEX in linux/capability.h: 176 func capToIndex(cap uintptr) uintptr { return cap >> 5 } 177 178 // See CAP_TO_MASK in linux/capability.h: 179 func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) } 180 181 // cloneArgs holds arguments for clone3 Linux syscall. 182 type cloneArgs struct { 183 flags uint64 // Flags bit mask 184 pidFD uint64 // Where to store PID file descriptor (int *) 185 childTID uint64 // Where to store child TID, in child's memory (pid_t *) 186 parentTID uint64 // Where to store child TID, in parent's memory (pid_t *) 187 exitSignal uint64 // Signal to deliver to parent on child termination 188 stack uint64 // Pointer to lowest byte of stack 189 stackSize uint64 // Size of stack 190 tls uint64 // Location of new TLS 191 setTID uint64 // Pointer to a pid_t array (since Linux 5.5) 192 setTIDSize uint64 // Number of elements in set_tid (since Linux 5.5) 193 cgroup uint64 // File descriptor for target cgroup of child (since Linux 5.7) 194 } 195 196 // forkAndExecInChild1 implements the body of forkAndExecInChild up to 197 // the parent's post-fork path. This is a separate function so we can 198 // separate the child's and parent's stack frames if we're using 199 // vfork. 200 // 201 // This is go:noinline because the point is to keep the stack frames 202 // of this and forkAndExecInChild separate. 203 // 204 //go:noinline 205 //go:norace 206 //go:nocheckptr 207 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) { 208 // Defined in linux/prctl.h starting with Linux 4.3. 209 const ( 210 PR_CAP_AMBIENT = 0x2f 211 PR_CAP_AMBIENT_RAISE = 0x2 212 ) 213 214 // vfork requires that the child not touch any of the parent's 215 // active stack frames. Hence, the child does all post-fork 216 // processing in this stack frame and never returns, while the 217 // parent returns immediately from this frame and does all 218 // post-fork processing in the outer frame. 219 // 220 // Declare all variables at top in case any 221 // declarations require heap allocation (e.g., err2). 222 // ":=" should not be used to declare any variable after 223 // the call to runtime_BeforeFork. 224 // 225 // NOTE(bcmills): The allocation behavior described in the above comment 226 // seems to lack a corresponding test, and it may be rendered invalid 227 // by an otherwise-correct change in the compiler. 228 var ( 229 err2 Errno 230 nextfd int 231 i int 232 caps caps 233 fd1, flags uintptr 234 puid, psetgroups, pgid []byte 235 uidmap, setgroups, gidmap []byte 236 clone3 *cloneArgs 237 pgrp int32 238 dirfd int 239 cred *Credential 240 ngroups, groups uintptr 241 c uintptr 242 ) 243 244 rlim, rlimOK := origRlimitNofile.Load().(Rlimit) 245 246 if sys.UidMappings != nil { 247 puid = []byte("/proc/self/uid_map\000") 248 uidmap = formatIDMappings(sys.UidMappings) 249 } 250 251 if sys.GidMappings != nil { 252 psetgroups = []byte("/proc/self/setgroups\000") 253 pgid = []byte("/proc/self/gid_map\000") 254 255 if sys.GidMappingsEnableSetgroups { 256 setgroups = []byte("allow\000") 257 } else { 258 setgroups = []byte("deny\000") 259 } 260 gidmap = formatIDMappings(sys.GidMappings) 261 } 262 263 // Record parent PID so child can test if it has died. 264 ppid, _ := rawSyscallNoError(SYS_GETPID, 0, 0, 0) 265 266 // Guard against side effects of shuffling fds below. 267 // Make sure that nextfd is beyond any currently open files so 268 // that we can't run the risk of overwriting any of them. 269 fd := make([]int, len(attr.Files)) 270 nextfd = len(attr.Files) 271 for i, ufd := range attr.Files { 272 if nextfd < int(ufd) { 273 nextfd = int(ufd) 274 } 275 fd[i] = int(ufd) 276 } 277 nextfd++ 278 279 // Allocate another pipe for parent to child communication for 280 // synchronizing writing of User ID/Group ID mappings. 281 if sys.UidMappings != nil || sys.GidMappings != nil { 282 if err := forkExecPipe(mapPipe[:]); err != nil { 283 err1 = err.(Errno) 284 return 285 } 286 } 287 288 flags = sys.Cloneflags 289 if sys.Cloneflags&CLONE_NEWUSER == 0 && sys.Unshareflags&CLONE_NEWUSER == 0 { 290 flags |= CLONE_VFORK | CLONE_VM 291 } 292 // Whether to use clone3. 293 if sys.UseCgroupFD { 294 clone3 = &cloneArgs{ 295 flags: uint64(flags) | CLONE_INTO_CGROUP, 296 exitSignal: uint64(SIGCHLD), 297 cgroup: uint64(sys.CgroupFD), 298 } 299 } else if flags&CLONE_NEWTIME != 0 { 300 clone3 = &cloneArgs{ 301 flags: uint64(flags), 302 exitSignal: uint64(SIGCHLD), 303 } 304 } 305 306 // About to call fork. 307 // No more allocation or calls of non-assembly functions. 308 runtime_BeforeFork() 309 locked = true 310 if clone3 != nil { 311 pid, err1 = rawVforkSyscall(_SYS_clone3, uintptr(unsafe.Pointer(clone3)), unsafe.Sizeof(*clone3)) 312 } else { 313 flags |= uintptr(SIGCHLD) 314 if runtime.GOARCH == "s390x" { 315 // On Linux/s390, the first two arguments of clone(2) are swapped. 316 pid, err1 = rawVforkSyscall(SYS_CLONE, 0, flags) 317 } else { 318 pid, err1 = rawVforkSyscall(SYS_CLONE, flags, 0) 319 } 320 } 321 if err1 != 0 || pid != 0 { 322 // If we're in the parent, we must return immediately 323 // so we're not in the same stack frame as the child. 324 // This can at most use the return PC, which the child 325 // will not modify, and the results of 326 // rawVforkSyscall, which must have been written after 327 // the child was replaced. 328 return 329 } 330 331 // Fork succeeded, now in child. 332 333 // Enable the "keep capabilities" flag to set ambient capabilities later. 334 if len(sys.AmbientCaps) > 0 { 335 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_KEEPCAPS, 1, 0, 0, 0, 0) 336 if err1 != 0 { 337 goto childerror 338 } 339 } 340 341 // Wait for User ID/Group ID mappings to be written. 342 if sys.UidMappings != nil || sys.GidMappings != nil { 343 if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(mapPipe[1]), 0, 0); err1 != 0 { 344 goto childerror 345 } 346 pid, _, err1 = RawSyscall(SYS_READ, uintptr(mapPipe[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2)) 347 if err1 != 0 { 348 goto childerror 349 } 350 if pid != unsafe.Sizeof(err2) { 351 err1 = EINVAL 352 goto childerror 353 } 354 if err2 != 0 { 355 err1 = err2 356 goto childerror 357 } 358 } 359 360 // Session ID 361 if sys.Setsid { 362 _, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0) 363 if err1 != 0 { 364 goto childerror 365 } 366 } 367 368 // Set process group 369 if sys.Setpgid || sys.Foreground { 370 // Place child in process group. 371 _, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0) 372 if err1 != 0 { 373 goto childerror 374 } 375 } 376 377 if sys.Foreground { 378 pgrp = int32(sys.Pgid) 379 if pgrp == 0 { 380 pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) 381 382 pgrp = int32(pid) 383 } 384 385 // Place process group in foreground. 386 _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp))) 387 if err1 != 0 { 388 goto childerror 389 } 390 } 391 392 // Restore the signal mask. We do this after TIOCSPGRP to avoid 393 // having the kernel send a SIGTTOU signal to the process group. 394 runtime_AfterForkInChild() 395 396 // Unshare 397 if sys.Unshareflags != 0 { 398 _, _, err1 = RawSyscall(SYS_UNSHARE, sys.Unshareflags, 0, 0) 399 if err1 != 0 { 400 goto childerror 401 } 402 403 if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.GidMappings != nil { 404 dirfd = int(_AT_FDCWD) 405 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&psetgroups[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 406 goto childerror 407 } 408 pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&setgroups[0])), uintptr(len(setgroups))) 409 if err1 != 0 { 410 goto childerror 411 } 412 if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { 413 goto childerror 414 } 415 416 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&pgid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 417 goto childerror 418 } 419 pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&gidmap[0])), uintptr(len(gidmap))) 420 if err1 != 0 { 421 goto childerror 422 } 423 if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { 424 goto childerror 425 } 426 } 427 428 if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.UidMappings != nil { 429 dirfd = int(_AT_FDCWD) 430 if fd1, _, err1 = RawSyscall6(SYS_OPENAT, uintptr(dirfd), uintptr(unsafe.Pointer(&puid[0])), uintptr(O_WRONLY), 0, 0, 0); err1 != 0 { 431 goto childerror 432 } 433 pid, _, err1 = RawSyscall(SYS_WRITE, uintptr(fd1), uintptr(unsafe.Pointer(&uidmap[0])), uintptr(len(uidmap))) 434 if err1 != 0 { 435 goto childerror 436 } 437 if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(fd1), 0, 0); err1 != 0 { 438 goto childerror 439 } 440 } 441 442 // The unshare system call in Linux doesn't unshare mount points 443 // mounted with --shared. Systemd mounts / with --shared. For a 444 // long discussion of the pros and cons of this see debian bug 739593. 445 // The Go model of unsharing is more like Plan 9, where you ask 446 // to unshare and the namespaces are unconditionally unshared. 447 // To make this model work we must further mark / as MS_PRIVATE. 448 // This is what the standard unshare command does. 449 if sys.Unshareflags&CLONE_NEWNS == CLONE_NEWNS { 450 _, _, err1 = RawSyscall6(SYS_MOUNT, uintptr(unsafe.Pointer(&none[0])), uintptr(unsafe.Pointer(&slash[0])), 0, MS_REC|MS_PRIVATE, 0, 0) 451 if err1 != 0 { 452 goto childerror 453 } 454 } 455 } 456 457 // Chroot 458 if chroot != nil { 459 _, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0) 460 if err1 != 0 { 461 goto childerror 462 } 463 } 464 465 // User and groups 466 if cred = sys.Credential; cred != nil { 467 ngroups = uintptr(len(cred.Groups)) 468 groups = uintptr(0) 469 if ngroups > 0 { 470 groups = uintptr(unsafe.Pointer(&cred.Groups[0])) 471 } 472 if !(sys.GidMappings != nil && !sys.GidMappingsEnableSetgroups && ngroups == 0) && !cred.NoSetGroups { 473 _, _, err1 = RawSyscall(_SYS_setgroups, ngroups, groups, 0) 474 if err1 != 0 { 475 goto childerror 476 } 477 } 478 _, _, err1 = RawSyscall(sys_SETGID, uintptr(cred.Gid), 0, 0) 479 if err1 != 0 { 480 goto childerror 481 } 482 _, _, err1 = RawSyscall(sys_SETUID, uintptr(cred.Uid), 0, 0) 483 if err1 != 0 { 484 goto childerror 485 } 486 } 487 488 if len(sys.AmbientCaps) != 0 { 489 // Ambient capabilities were added in the 4.3 kernel, 490 // so it is safe to always use _LINUX_CAPABILITY_VERSION_3. 491 caps.hdr.version = _LINUX_CAPABILITY_VERSION_3 492 493 if _, _, err1 = RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { 494 goto childerror 495 } 496 497 for _, c = range sys.AmbientCaps { 498 // Add the c capability to the permitted and inheritable capability mask, 499 // otherwise we will not be able to add it to the ambient capability mask. 500 caps.data[capToIndex(c)].permitted |= capToMask(c) 501 caps.data[capToIndex(c)].inheritable |= capToMask(c) 502 } 503 504 if _, _, err1 = RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 { 505 goto childerror 506 } 507 508 for _, c = range sys.AmbientCaps { 509 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0) 510 if err1 != 0 { 511 goto childerror 512 } 513 } 514 } 515 516 // Chdir 517 if dir != nil { 518 _, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0) 519 if err1 != 0 { 520 goto childerror 521 } 522 } 523 524 // Parent death signal 525 if sys.Pdeathsig != 0 { 526 _, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 0, 0, 0) 527 if err1 != 0 { 528 goto childerror 529 } 530 531 // Signal self if parent is already dead. This might cause a 532 // duplicate signal in rare cases, but it won't matter when 533 // using SIGKILL. 534 pid, _ = rawSyscallNoError(SYS_GETPPID, 0, 0, 0) 535 if pid != ppid { 536 pid, _ = rawSyscallNoError(SYS_GETPID, 0, 0, 0) 537 _, _, err1 = RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0) 538 if err1 != 0 { 539 goto childerror 540 } 541 } 542 } 543 544 // Pass 1: look for fd[i] < i and move those up above len(fd) 545 // so that pass 2 won't stomp on an fd it needs later. 546 if pipe < nextfd { 547 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(pipe), uintptr(nextfd), O_CLOEXEC) 548 if err1 != 0 { 549 goto childerror 550 } 551 pipe = nextfd 552 nextfd++ 553 } 554 for i = 0; i < len(fd); i++ { 555 if fd[i] >= 0 && fd[i] < i { 556 if nextfd == pipe { // don't stomp on pipe 557 nextfd++ 558 } 559 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC) 560 if err1 != 0 { 561 goto childerror 562 } 563 fd[i] = nextfd 564 nextfd++ 565 } 566 } 567 568 // Pass 2: dup fd[i] down onto i. 569 for i = 0; i < len(fd); i++ { 570 if fd[i] == -1 { 571 RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) 572 continue 573 } 574 if fd[i] == i { 575 // dup2(i, i) won't clear close-on-exec flag on Linux, 576 // probably not elsewhere either. 577 _, _, err1 = RawSyscall(fcntl64Syscall, uintptr(fd[i]), F_SETFD, 0) 578 if err1 != 0 { 579 goto childerror 580 } 581 continue 582 } 583 // The new fd is created NOT close-on-exec, 584 // which is exactly what we want. 585 _, _, err1 = RawSyscall(SYS_DUP3, uintptr(fd[i]), uintptr(i), 0) 586 if err1 != 0 { 587 goto childerror 588 } 589 } 590 591 // By convention, we don't close-on-exec the fds we are 592 // started with, so if len(fd) < 3, close 0, 1, 2 as needed. 593 // Programs that know they inherit fds >= 3 will need 594 // to set them close-on-exec. 595 for i = len(fd); i < 3; i++ { 596 RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) 597 } 598 599 // Detach fd 0 from tty 600 if sys.Noctty { 601 _, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0) 602 if err1 != 0 { 603 goto childerror 604 } 605 } 606 607 // Set the controlling TTY to Ctty 608 if sys.Setctty { 609 _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 1) 610 if err1 != 0 { 611 goto childerror 612 } 613 } 614 615 // Restore original rlimit. 616 if rlimOK && rlim.Cur != 0 { 617 rawSetrlimit(RLIMIT_NOFILE, &rlim) 618 } 619 620 // Enable tracing if requested. 621 // Do this right before exec so that we don't unnecessarily trace the runtime 622 // setting up after the fork. See issue #21428. 623 if sys.Ptrace { 624 _, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0) 625 if err1 != 0 { 626 goto childerror 627 } 628 } 629 630 // Time to exec. 631 _, _, err1 = RawSyscall(SYS_EXECVE, 632 uintptr(unsafe.Pointer(argv0)), 633 uintptr(unsafe.Pointer(&argv[0])), 634 uintptr(unsafe.Pointer(&envv[0]))) 635 636 childerror: 637 // send error code on pipe 638 RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1)) 639 for { 640 RawSyscall(SYS_EXIT, 253, 0, 0) 641 } 642 } 643 644 // Try to open a pipe with O_CLOEXEC set on both file descriptors. 645 func forkExecPipe(p []int) (err error) { 646 return Pipe2(p, O_CLOEXEC) 647 } 648 649 func formatIDMappings(idMap []SysProcIDMap) []byte { 650 var data []byte 651 for _, im := range idMap { 652 data = append(data, itoa.Itoa(im.ContainerID)+" "+itoa.Itoa(im.HostID)+" "+itoa.Itoa(im.Size)+"\n"...) 653 } 654 return data 655 } 656 657 // writeIDMappings writes the user namespace User ID or Group ID mappings to the specified path. 658 func writeIDMappings(path string, idMap []SysProcIDMap) error { 659 fd, err := Open(path, O_RDWR, 0) 660 if err != nil { 661 return err 662 } 663 664 if _, err := Write(fd, formatIDMappings(idMap)); err != nil { 665 Close(fd) 666 return err 667 } 668 669 if err := Close(fd); err != nil { 670 return err 671 } 672 673 return nil 674 } 675 676 // writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false 677 // and "allow" if enable is true. 678 // This is needed since kernel 3.19, because you can't write gid_map without 679 // disabling setgroups() system call. 680 func writeSetgroups(pid int, enable bool) error { 681 sgf := "/proc/" + itoa.Itoa(pid) + "/setgroups" 682 fd, err := Open(sgf, O_RDWR, 0) 683 if err != nil { 684 return err 685 } 686 687 var data []byte 688 if enable { 689 data = []byte("allow") 690 } else { 691 data = []byte("deny") 692 } 693 694 if _, err := Write(fd, data); err != nil { 695 Close(fd) 696 return err 697 } 698 699 return Close(fd) 700 } 701 702 // writeUidGidMappings writes User ID and Group ID mappings for user namespaces 703 // for a process and it is called from the parent process. 704 func writeUidGidMappings(pid int, sys *SysProcAttr) error { 705 if sys.UidMappings != nil { 706 uidf := "/proc/" + itoa.Itoa(pid) + "/uid_map" 707 if err := writeIDMappings(uidf, sys.UidMappings); err != nil { 708 return err 709 } 710 } 711 712 if sys.GidMappings != nil { 713 // If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK. 714 if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT { 715 return err 716 } 717 gidf := "/proc/" + itoa.Itoa(pid) + "/gid_map" 718 if err := writeIDMappings(gidf, sys.GidMappings); err != nil { 719 return err 720 } 721 } 722 723 return nil 724 }