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path: root/pkg/sentry/syscalls/linux/vfs2/poll.go
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Diffstat (limited to 'pkg/sentry/syscalls/linux/vfs2/poll.go')
-rw-r--r--pkg/sentry/syscalls/linux/vfs2/poll.go584
1 files changed, 584 insertions, 0 deletions
diff --git a/pkg/sentry/syscalls/linux/vfs2/poll.go b/pkg/sentry/syscalls/linux/vfs2/poll.go
new file mode 100644
index 000000000..dbf4882da
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/vfs2/poll.go
@@ -0,0 +1,584 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vfs2
+
+import (
+ "fmt"
+ "time"
+
+ "gvisor.dev/gvisor/pkg/abi/linux"
+ "gvisor.dev/gvisor/pkg/sentry/arch"
+ "gvisor.dev/gvisor/pkg/sentry/kernel"
+ ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
+ "gvisor.dev/gvisor/pkg/sentry/limits"
+ "gvisor.dev/gvisor/pkg/sentry/vfs"
+ "gvisor.dev/gvisor/pkg/syserror"
+ "gvisor.dev/gvisor/pkg/usermem"
+ "gvisor.dev/gvisor/pkg/waiter"
+)
+
+// fileCap is the maximum allowable files for poll & select. This has no
+// equivalent in Linux; it exists in gVisor since allocation failure in Go is
+// unrecoverable.
+const fileCap = 1024 * 1024
+
+// Masks for "readable", "writable", and "exceptional" events as defined by
+// select(2).
+const (
+ // selectReadEvents is analogous to the Linux kernel's
+ // fs/select.c:POLLIN_SET.
+ selectReadEvents = linux.POLLIN | linux.POLLHUP | linux.POLLERR
+
+ // selectWriteEvents is analogous to the Linux kernel's
+ // fs/select.c:POLLOUT_SET.
+ selectWriteEvents = linux.POLLOUT | linux.POLLERR
+
+ // selectExceptEvents is analogous to the Linux kernel's
+ // fs/select.c:POLLEX_SET.
+ selectExceptEvents = linux.POLLPRI
+)
+
+// pollState tracks the associated file description and waiter of a PollFD.
+type pollState struct {
+ file *vfs.FileDescription
+ waiter waiter.Entry
+}
+
+// initReadiness gets the current ready mask for the file represented by the FD
+// stored in pfd.FD. If a channel is passed in, the waiter entry in "state" is
+// used to register with the file for event notifications, and a reference to
+// the file is stored in "state".
+func initReadiness(t *kernel.Task, pfd *linux.PollFD, state *pollState, ch chan struct{}) {
+ if pfd.FD < 0 {
+ pfd.REvents = 0
+ return
+ }
+
+ file := t.GetFileVFS2(pfd.FD)
+ if file == nil {
+ pfd.REvents = linux.POLLNVAL
+ return
+ }
+
+ if ch == nil {
+ defer file.DecRef()
+ } else {
+ state.file = file
+ state.waiter, _ = waiter.NewChannelEntry(ch)
+ file.EventRegister(&state.waiter, waiter.EventMaskFromLinux(uint32(pfd.Events)))
+ }
+
+ r := file.Readiness(waiter.EventMaskFromLinux(uint32(pfd.Events)))
+ pfd.REvents = int16(r.ToLinux()) & pfd.Events
+}
+
+// releaseState releases all the pollState in "state".
+func releaseState(state []pollState) {
+ for i := range state {
+ if state[i].file != nil {
+ state[i].file.EventUnregister(&state[i].waiter)
+ state[i].file.DecRef()
+ }
+ }
+}
+
+// pollBlock polls the PollFDs in "pfd" with a bounded time specified in "timeout"
+// when "timeout" is greater than zero.
+//
+// pollBlock returns the remaining timeout, which is always 0 on a timeout; and 0 or
+// positive if interrupted by a signal.
+func pollBlock(t *kernel.Task, pfd []linux.PollFD, timeout time.Duration) (time.Duration, uintptr, error) {
+ var ch chan struct{}
+ if timeout != 0 {
+ ch = make(chan struct{}, 1)
+ }
+
+ // Register for event notification in the files involved if we may
+ // block (timeout not zero). Once we find a file that has a non-zero
+ // result, we stop registering for events but still go through all files
+ // to get their ready masks.
+ state := make([]pollState, len(pfd))
+ defer releaseState(state)
+ n := uintptr(0)
+ for i := range pfd {
+ initReadiness(t, &pfd[i], &state[i], ch)
+ if pfd[i].REvents != 0 {
+ n++
+ ch = nil
+ }
+ }
+
+ if timeout == 0 {
+ return timeout, n, nil
+ }
+
+ haveTimeout := timeout >= 0
+
+ for n == 0 {
+ var err error
+ // Wait for a notification.
+ timeout, err = t.BlockWithTimeout(ch, haveTimeout, timeout)
+ if err != nil {
+ if err == syserror.ETIMEDOUT {
+ err = nil
+ }
+ return timeout, 0, err
+ }
+
+ // We got notified, count how many files are ready. If none,
+ // then this was a spurious notification, and we just go back
+ // to sleep with the remaining timeout.
+ for i := range state {
+ if state[i].file == nil {
+ continue
+ }
+
+ r := state[i].file.Readiness(waiter.EventMaskFromLinux(uint32(pfd[i].Events)))
+ rl := int16(r.ToLinux()) & pfd[i].Events
+ if rl != 0 {
+ pfd[i].REvents = rl
+ n++
+ }
+ }
+ }
+
+ return timeout, n, nil
+}
+
+// copyInPollFDs copies an array of struct pollfd unless nfds exceeds the max.
+func copyInPollFDs(t *kernel.Task, addr usermem.Addr, nfds uint) ([]linux.PollFD, error) {
+ if uint64(nfds) > t.ThreadGroup().Limits().GetCapped(limits.NumberOfFiles, fileCap) {
+ return nil, syserror.EINVAL
+ }
+
+ pfd := make([]linux.PollFD, nfds)
+ if nfds > 0 {
+ if _, err := t.CopyIn(addr, &pfd); err != nil {
+ return nil, err
+ }
+ }
+
+ return pfd, nil
+}
+
+func doPoll(t *kernel.Task, addr usermem.Addr, nfds uint, timeout time.Duration) (time.Duration, uintptr, error) {
+ pfd, err := copyInPollFDs(t, addr, nfds)
+ if err != nil {
+ return timeout, 0, err
+ }
+
+ // Compatibility warning: Linux adds POLLHUP and POLLERR just before
+ // polling, in fs/select.c:do_pollfd(). Since pfd is copied out after
+ // polling, changing event masks here is an application-visible difference.
+ // (Linux also doesn't copy out event masks at all, only revents.)
+ for i := range pfd {
+ pfd[i].Events |= linux.POLLHUP | linux.POLLERR
+ }
+ remainingTimeout, n, err := pollBlock(t, pfd, timeout)
+ err = syserror.ConvertIntr(err, syserror.EINTR)
+
+ // The poll entries are copied out regardless of whether
+ // any are set or not. This aligns with the Linux behavior.
+ if nfds > 0 && err == nil {
+ if _, err := t.CopyOut(addr, pfd); err != nil {
+ return remainingTimeout, 0, err
+ }
+ }
+
+ return remainingTimeout, n, err
+}
+
+// CopyInFDSet copies an fd set from select(2)/pselect(2).
+func CopyInFDSet(t *kernel.Task, addr usermem.Addr, nBytes, nBitsInLastPartialByte int) ([]byte, error) {
+ set := make([]byte, nBytes)
+
+ if addr != 0 {
+ if _, err := t.CopyIn(addr, &set); err != nil {
+ return nil, err
+ }
+ // If we only use part of the last byte, mask out the extraneous bits.
+ //
+ // N.B. This only works on little-endian architectures.
+ if nBitsInLastPartialByte != 0 {
+ set[nBytes-1] &^= byte(0xff) << nBitsInLastPartialByte
+ }
+ }
+ return set, nil
+}
+
+func doSelect(t *kernel.Task, nfds int, readFDs, writeFDs, exceptFDs usermem.Addr, timeout time.Duration) (uintptr, error) {
+ if nfds < 0 || nfds > fileCap {
+ return 0, syserror.EINVAL
+ }
+
+ // Calculate the size of the fd sets (one bit per fd).
+ nBytes := (nfds + 7) / 8
+ nBitsInLastPartialByte := nfds % 8
+
+ // Capture all the provided input vectors.
+ r, err := CopyInFDSet(t, readFDs, nBytes, nBitsInLastPartialByte)
+ if err != nil {
+ return 0, err
+ }
+ w, err := CopyInFDSet(t, writeFDs, nBytes, nBitsInLastPartialByte)
+ if err != nil {
+ return 0, err
+ }
+ e, err := CopyInFDSet(t, exceptFDs, nBytes, nBitsInLastPartialByte)
+ if err != nil {
+ return 0, err
+ }
+
+ // Count how many FDs are actually being requested so that we can build
+ // a PollFD array.
+ fdCount := 0
+ for i := 0; i < nBytes; i++ {
+ v := r[i] | w[i] | e[i]
+ for v != 0 {
+ v &= (v - 1)
+ fdCount++
+ }
+ }
+
+ // Build the PollFD array.
+ pfd := make([]linux.PollFD, 0, fdCount)
+ var fd int32
+ for i := 0; i < nBytes; i++ {
+ rV, wV, eV := r[i], w[i], e[i]
+ v := rV | wV | eV
+ m := byte(1)
+ for j := 0; j < 8; j++ {
+ if (v & m) != 0 {
+ // Make sure the fd is valid and decrement the reference
+ // immediately to ensure we don't leak. Note, another thread
+ // might be about to close fd. This is racy, but that's
+ // OK. Linux is racy in the same way.
+ file := t.GetFileVFS2(fd)
+ if file == nil {
+ return 0, syserror.EBADF
+ }
+ file.DecRef()
+
+ var mask int16
+ if (rV & m) != 0 {
+ mask |= selectReadEvents
+ }
+
+ if (wV & m) != 0 {
+ mask |= selectWriteEvents
+ }
+
+ if (eV & m) != 0 {
+ mask |= selectExceptEvents
+ }
+
+ pfd = append(pfd, linux.PollFD{
+ FD: fd,
+ Events: mask,
+ })
+ }
+
+ fd++
+ m <<= 1
+ }
+ }
+
+ // Do the syscall, then count the number of bits set.
+ if _, _, err = pollBlock(t, pfd, timeout); err != nil {
+ return 0, syserror.ConvertIntr(err, syserror.EINTR)
+ }
+
+ // r, w, and e are currently event mask bitsets; unset bits corresponding
+ // to events that *didn't* occur.
+ bitSetCount := uintptr(0)
+ for idx := range pfd {
+ events := pfd[idx].REvents
+ i, j := pfd[idx].FD/8, uint(pfd[idx].FD%8)
+ m := byte(1) << j
+ if r[i]&m != 0 {
+ if (events & selectReadEvents) != 0 {
+ bitSetCount++
+ } else {
+ r[i] &^= m
+ }
+ }
+ if w[i]&m != 0 {
+ if (events & selectWriteEvents) != 0 {
+ bitSetCount++
+ } else {
+ w[i] &^= m
+ }
+ }
+ if e[i]&m != 0 {
+ if (events & selectExceptEvents) != 0 {
+ bitSetCount++
+ } else {
+ e[i] &^= m
+ }
+ }
+ }
+
+ // Copy updated vectors back.
+ if readFDs != 0 {
+ if _, err := t.CopyOut(readFDs, r); err != nil {
+ return 0, err
+ }
+ }
+
+ if writeFDs != 0 {
+ if _, err := t.CopyOut(writeFDs, w); err != nil {
+ return 0, err
+ }
+ }
+
+ if exceptFDs != 0 {
+ if _, err := t.CopyOut(exceptFDs, e); err != nil {
+ return 0, err
+ }
+ }
+
+ return bitSetCount, nil
+}
+
+// timeoutRemaining returns the amount of time remaining for the specified
+// timeout or 0 if it has elapsed.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func timeoutRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration) time.Duration {
+ now := t.Kernel().MonotonicClock().Now()
+ remaining := timeout - now.Sub(startNs)
+ if remaining < 0 {
+ remaining = 0
+ }
+ return remaining
+}
+
+// copyOutTimespecRemaining copies the time remaining in timeout to timespecAddr.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func copyOutTimespecRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration, timespecAddr usermem.Addr) error {
+ if timeout <= 0 {
+ return nil
+ }
+ remaining := timeoutRemaining(t, startNs, timeout)
+ tsRemaining := linux.NsecToTimespec(remaining.Nanoseconds())
+ return tsRemaining.CopyOut(t, timespecAddr)
+}
+
+// copyOutTimevalRemaining copies the time remaining in timeout to timevalAddr.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func copyOutTimevalRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration, timevalAddr usermem.Addr) error {
+ if timeout <= 0 {
+ return nil
+ }
+ remaining := timeoutRemaining(t, startNs, timeout)
+ tvRemaining := linux.NsecToTimeval(remaining.Nanoseconds())
+ return tvRemaining.CopyOut(t, timevalAddr)
+}
+
+// pollRestartBlock encapsulates the state required to restart poll(2) via
+// restart_syscall(2).
+//
+// +stateify savable
+type pollRestartBlock struct {
+ pfdAddr usermem.Addr
+ nfds uint
+ timeout time.Duration
+}
+
+// Restart implements kernel.SyscallRestartBlock.Restart.
+func (p *pollRestartBlock) Restart(t *kernel.Task) (uintptr, error) {
+ return poll(t, p.pfdAddr, p.nfds, p.timeout)
+}
+
+func poll(t *kernel.Task, pfdAddr usermem.Addr, nfds uint, timeout time.Duration) (uintptr, error) {
+ remainingTimeout, n, err := doPoll(t, pfdAddr, nfds, timeout)
+ // On an interrupt poll(2) is restarted with the remaining timeout.
+ if err == syserror.EINTR {
+ t.SetSyscallRestartBlock(&pollRestartBlock{
+ pfdAddr: pfdAddr,
+ nfds: nfds,
+ timeout: remainingTimeout,
+ })
+ return 0, kernel.ERESTART_RESTARTBLOCK
+ }
+ return n, err
+}
+
+// Poll implements linux syscall poll(2).
+func Poll(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+ pfdAddr := args[0].Pointer()
+ nfds := uint(args[1].Uint()) // poll(2) uses unsigned long.
+ timeout := time.Duration(args[2].Int()) * time.Millisecond
+ n, err := poll(t, pfdAddr, nfds, timeout)
+ return n, nil, err
+}
+
+// Ppoll implements linux syscall ppoll(2).
+func Ppoll(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+ pfdAddr := args[0].Pointer()
+ nfds := uint(args[1].Uint()) // poll(2) uses unsigned long.
+ timespecAddr := args[2].Pointer()
+ maskAddr := args[3].Pointer()
+ maskSize := uint(args[4].Uint())
+
+ timeout, err := copyTimespecInToDuration(t, timespecAddr)
+ if err != nil {
+ return 0, nil, err
+ }
+
+ var startNs ktime.Time
+ if timeout > 0 {
+ startNs = t.Kernel().MonotonicClock().Now()
+ }
+
+ if err := setTempSignalSet(t, maskAddr, maskSize); err != nil {
+ return 0, nil, err
+ }
+
+ _, n, err := doPoll(t, pfdAddr, nfds, timeout)
+ copyErr := copyOutTimespecRemaining(t, startNs, timeout, timespecAddr)
+ // doPoll returns EINTR if interrupted, but ppoll is normally restartable
+ // if interrupted by something other than a signal handled by the
+ // application (i.e. returns ERESTARTNOHAND). However, if
+ // copyOutTimespecRemaining failed, then the restarted ppoll would use the
+ // wrong timeout, so the error should be left as EINTR.
+ //
+ // Note that this means that if err is nil but copyErr is not, copyErr is
+ // ignored. This is consistent with Linux.
+ if err == syserror.EINTR && copyErr == nil {
+ err = kernel.ERESTARTNOHAND
+ }
+ return n, nil, err
+}
+
+// Select implements linux syscall select(2).
+func Select(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+ nfds := int(args[0].Int()) // select(2) uses an int.
+ readFDs := args[1].Pointer()
+ writeFDs := args[2].Pointer()
+ exceptFDs := args[3].Pointer()
+ timevalAddr := args[4].Pointer()
+
+ // Use a negative Duration to indicate "no timeout".
+ timeout := time.Duration(-1)
+ if timevalAddr != 0 {
+ var timeval linux.Timeval
+ if err := timeval.CopyIn(t, timevalAddr); err != nil {
+ return 0, nil, err
+ }
+ if timeval.Sec < 0 || timeval.Usec < 0 {
+ return 0, nil, syserror.EINVAL
+ }
+ timeout = time.Duration(timeval.ToNsecCapped())
+ }
+ startNs := t.Kernel().MonotonicClock().Now()
+ n, err := doSelect(t, nfds, readFDs, writeFDs, exceptFDs, timeout)
+ copyErr := copyOutTimevalRemaining(t, startNs, timeout, timevalAddr)
+ // See comment in Ppoll.
+ if err == syserror.EINTR && copyErr == nil {
+ err = kernel.ERESTARTNOHAND
+ }
+ return n, nil, err
+}
+
+// Pselect implements linux syscall pselect(2).
+func Pselect(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+ nfds := int(args[0].Int()) // select(2) uses an int.
+ readFDs := args[1].Pointer()
+ writeFDs := args[2].Pointer()
+ exceptFDs := args[3].Pointer()
+ timespecAddr := args[4].Pointer()
+ maskWithSizeAddr := args[5].Pointer()
+
+ timeout, err := copyTimespecInToDuration(t, timespecAddr)
+ if err != nil {
+ return 0, nil, err
+ }
+
+ var startNs ktime.Time
+ if timeout > 0 {
+ startNs = t.Kernel().MonotonicClock().Now()
+ }
+
+ if maskWithSizeAddr != 0 {
+ if t.Arch().Width() != 8 {
+ panic(fmt.Sprintf("unsupported sizeof(void*): %d", t.Arch().Width()))
+ }
+ var maskStruct sigSetWithSize
+ if err := maskStruct.CopyIn(t, maskWithSizeAddr); err != nil {
+ return 0, nil, err
+ }
+ if err := setTempSignalSet(t, usermem.Addr(maskStruct.sigsetAddr), uint(maskStruct.sizeofSigset)); err != nil {
+ return 0, nil, err
+ }
+ }
+
+ n, err := doSelect(t, nfds, readFDs, writeFDs, exceptFDs, timeout)
+ copyErr := copyOutTimespecRemaining(t, startNs, timeout, timespecAddr)
+ // See comment in Ppoll.
+ if err == syserror.EINTR && copyErr == nil {
+ err = kernel.ERESTARTNOHAND
+ }
+ return n, nil, err
+}
+
+// +marshal
+type sigSetWithSize struct {
+ sigsetAddr uint64
+ sizeofSigset uint64
+}
+
+// copyTimespecInToDuration copies a Timespec from the untrusted app range,
+// validates it and converts it to a Duration.
+//
+// If the Timespec is larger than what can be represented in a Duration, the
+// returned value is the maximum that Duration will allow.
+//
+// If timespecAddr is NULL, the returned value is negative.
+func copyTimespecInToDuration(t *kernel.Task, timespecAddr usermem.Addr) (time.Duration, error) {
+ // Use a negative Duration to indicate "no timeout".
+ timeout := time.Duration(-1)
+ if timespecAddr != 0 {
+ var timespec linux.Timespec
+ if err := timespec.CopyIn(t, timespecAddr); err != nil {
+ return 0, err
+ }
+ if !timespec.Valid() {
+ return 0, syserror.EINVAL
+ }
+ timeout = time.Duration(timespec.ToNsecCapped())
+ }
+ return timeout, nil
+}
+
+func setTempSignalSet(t *kernel.Task, maskAddr usermem.Addr, maskSize uint) error {
+ if maskAddr == 0 {
+ return nil
+ }
+ if maskSize != linux.SignalSetSize {
+ return syserror.EINVAL
+ }
+ var mask linux.SignalSet
+ if err := mask.CopyIn(t, maskAddr); err != nil {
+ return err
+ }
+ mask &^= kernel.UnblockableSignals
+ oldmask := t.SignalMask()
+ t.SetSignalMask(mask)
+ t.SetSavedSignalMask(oldmask)
+ return nil
+}
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