Implement splice(2) and tee(2) for VFS2.

Updates #138

PiperOrigin-RevId: 313326354

3 files changed, 289 insertions, 2 deletions

diff --git a/pkg/sentry/syscalls/linux/vfs2/BUILD b/pkg/sentry/syscalls/linux/vfs2/BUILD
index f882ef840..d56927ff5 100644
--- a/pkg/sentry/syscalls/linux/vfs2/BUILD
+++ b/pkg/sentry/syscalls/linux/vfs2/BUILD
@@ -22,6 +22,7 @@ go_library(
         "setstat.go",
         "signal.go",
         "socket.go",
+        "splice.go",
         "stat.go",
         "stat_amd64.go",
         "stat_arm64.go",
diff --git a/pkg/sentry/syscalls/linux/vfs2/splice.go b/pkg/sentry/syscalls/linux/vfs2/splice.go
new file mode 100644
index 000000000..8f3c22a02
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/vfs2/splice.go
@@ -0,0 +1,286 @@
+// 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 (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/pipe"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// Splice implements Linux syscall splice(2).
+func Splice(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	inFD := args[0].Int()
+	inOffsetPtr := args[1].Pointer()
+	outFD := args[2].Int()
+	outOffsetPtr := args[3].Pointer()
+	count := int64(args[4].SizeT())
+	flags := args[5].Int()
+
+	if count == 0 {
+		return 0, nil, nil
+	}
+	if count > int64(kernel.MAX_RW_COUNT) {
+		count = int64(kernel.MAX_RW_COUNT)
+	}
+
+	// Check for invalid flags.
+	if flags&^(linux.SPLICE_F_MOVE|linux.SPLICE_F_NONBLOCK|linux.SPLICE_F_MORE|linux.SPLICE_F_GIFT) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Get file descriptions.
+	inFile := t.GetFileVFS2(inFD)
+	if inFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer inFile.DecRef()
+	outFile := t.GetFileVFS2(outFD)
+	if outFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer outFile.DecRef()
+
+	// Check that both files support the required directionality.
+	if !inFile.IsReadable() || !outFile.IsWritable() {
+		return 0, nil, syserror.EBADF
+	}
+
+	// The operation is non-blocking if anything is non-blocking.
+	//
+	// N.B. This is a rather simplistic heuristic that avoids some
+	// poor edge case behavior since the exact semantics here are
+	// underspecified and vary between versions of Linux itself.
+	nonBlock := ((inFile.StatusFlags()|outFile.StatusFlags())&linux.O_NONBLOCK != 0) || (flags&linux.SPLICE_F_NONBLOCK != 0)
+
+	// At least one file description must represent a pipe.
+	inPipeFD, inIsPipe := inFile.Impl().(*pipe.VFSPipeFD)
+	outPipeFD, outIsPipe := outFile.Impl().(*pipe.VFSPipeFD)
+	if !inIsPipe && !outIsPipe {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Copy in offsets.
+	inOffset := int64(-1)
+	if inOffsetPtr != 0 {
+		if inIsPipe {
+			return 0, nil, syserror.ESPIPE
+		}
+		if inFile.Options().DenyPRead {
+			return 0, nil, syserror.EINVAL
+		}
+		if _, err := t.CopyIn(inOffsetPtr, &inOffset); err != nil {
+			return 0, nil, err
+		}
+		if inOffset < 0 {
+			return 0, nil, syserror.EINVAL
+		}
+	}
+	outOffset := int64(-1)
+	if outOffsetPtr != 0 {
+		if outIsPipe {
+			return 0, nil, syserror.ESPIPE
+		}
+		if outFile.Options().DenyPWrite {
+			return 0, nil, syserror.EINVAL
+		}
+		if _, err := t.CopyIn(outOffsetPtr, &outOffset); err != nil {
+			return 0, nil, err
+		}
+		if outOffset < 0 {
+			return 0, nil, syserror.EINVAL
+		}
+	}
+
+	// Move data.
+	var (
+		n     int64
+		err   error
+		inCh  chan struct{}
+		outCh chan struct{}
+	)
+	for {
+		// If both input and output are pipes, delegate to the pipe
+		// implementation. Otherwise, exactly one end is a pipe, which we
+		// ensure is consistently ordered after the non-pipe FD's locks by
+		// passing the pipe FD as usermem.IO to the non-pipe end.
+		switch {
+		case inIsPipe && outIsPipe:
+			n, err = pipe.Splice(t, outPipeFD, inPipeFD, count)
+		case inIsPipe:
+			if outOffset != -1 {
+				n, err = outFile.PWrite(t, inPipeFD.IOSequence(count), outOffset, vfs.WriteOptions{})
+				outOffset += n
+			} else {
+				n, err = outFile.Write(t, inPipeFD.IOSequence(count), vfs.WriteOptions{})
+			}
+		case outIsPipe:
+			if inOffset != -1 {
+				n, err = inFile.PRead(t, outPipeFD.IOSequence(count), inOffset, vfs.ReadOptions{})
+				inOffset += n
+			} else {
+				n, err = inFile.Read(t, outPipeFD.IOSequence(count), vfs.ReadOptions{})
+			}
+		}
+		if n != 0 || err != syserror.ErrWouldBlock || nonBlock {
+			break
+		}
+
+		// Note that the blocking behavior here is a bit different than the
+		// normal pattern. Because we need to have both data to read and data
+		// to write simultaneously, we actually explicitly block on both of
+		// these cases in turn before returning to the splice operation.
+		if inFile.Readiness(eventMaskRead)&eventMaskRead == 0 {
+			if inCh == nil {
+				inCh = make(chan struct{}, 1)
+				inW, _ := waiter.NewChannelEntry(inCh)
+				inFile.EventRegister(&inW, eventMaskRead)
+				defer inFile.EventUnregister(&inW)
+				continue // Need to refresh readiness.
+			}
+			if err = t.Block(inCh); err != nil {
+				break
+			}
+		}
+		if outFile.Readiness(eventMaskWrite)&eventMaskWrite == 0 {
+			if outCh == nil {
+				outCh = make(chan struct{}, 1)
+				outW, _ := waiter.NewChannelEntry(outCh)
+				outFile.EventRegister(&outW, eventMaskWrite)
+				defer outFile.EventUnregister(&outW)
+				continue // Need to refresh readiness.
+			}
+			if err = t.Block(outCh); err != nil {
+				break
+			}
+		}
+	}
+
+	// Copy updated offsets out.
+	if inOffsetPtr != 0 {
+		if _, err := t.CopyOut(inOffsetPtr, &inOffset); err != nil {
+			return 0, nil, err
+		}
+	}
+	if outOffsetPtr != 0 {
+		if _, err := t.CopyOut(outOffsetPtr, &outOffset); err != nil {
+			return 0, nil, err
+		}
+	}
+
+	if n == 0 {
+		return 0, nil, err
+	}
+	return uintptr(n), nil, nil
+}
+
+// Tee implements Linux syscall tee(2).
+func Tee(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	inFD := args[0].Int()
+	outFD := args[1].Int()
+	count := int64(args[2].SizeT())
+	flags := args[3].Int()
+
+	if count == 0 {
+		return 0, nil, nil
+	}
+	if count > int64(kernel.MAX_RW_COUNT) {
+		count = int64(kernel.MAX_RW_COUNT)
+	}
+
+	// Check for invalid flags.
+	if flags&^(linux.SPLICE_F_MOVE|linux.SPLICE_F_NONBLOCK|linux.SPLICE_F_MORE|linux.SPLICE_F_GIFT) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Get file descriptions.
+	inFile := t.GetFileVFS2(inFD)
+	if inFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer inFile.DecRef()
+	outFile := t.GetFileVFS2(outFD)
+	if outFile == nil {
+		return 0, nil, syserror.EBADF
+	}
+	defer outFile.DecRef()
+
+	// Check that both files support the required directionality.
+	if !inFile.IsReadable() || !outFile.IsWritable() {
+		return 0, nil, syserror.EBADF
+	}
+
+	// The operation is non-blocking if anything is non-blocking.
+	//
+	// N.B. This is a rather simplistic heuristic that avoids some
+	// poor edge case behavior since the exact semantics here are
+	// underspecified and vary between versions of Linux itself.
+	nonBlock := ((inFile.StatusFlags()|outFile.StatusFlags())&linux.O_NONBLOCK != 0) || (flags&linux.SPLICE_F_NONBLOCK != 0)
+
+	// Both file descriptions must represent pipes.
+	inPipeFD, inIsPipe := inFile.Impl().(*pipe.VFSPipeFD)
+	outPipeFD, outIsPipe := outFile.Impl().(*pipe.VFSPipeFD)
+	if !inIsPipe || !outIsPipe {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Copy data.
+	var (
+		inCh  chan struct{}
+		outCh chan struct{}
+	)
+	for {
+		n, err := pipe.Tee(t, outPipeFD, inPipeFD, count)
+		if n != 0 {
+			return uintptr(n), nil, nil
+		}
+		if err != syserror.ErrWouldBlock || nonBlock {
+			return 0, nil, err
+		}
+
+		// Note that the blocking behavior here is a bit different than the
+		// normal pattern. Because we need to have both data to read and data
+		// to write simultaneously, we actually explicitly block on both of
+		// these cases in turn before returning to the tee operation.
+		if inFile.Readiness(eventMaskRead)&eventMaskRead == 0 {
+			if inCh == nil {
+				inCh = make(chan struct{}, 1)
+				inW, _ := waiter.NewChannelEntry(inCh)
+				inFile.EventRegister(&inW, eventMaskRead)
+				defer inFile.EventUnregister(&inW)
+				continue // Need to refresh readiness.
+			}
+			if err := t.Block(inCh); err != nil {
+				return 0, nil, err
+			}
+		}
+		if outFile.Readiness(eventMaskWrite)&eventMaskWrite == 0 {
+			if outCh == nil {
+				outCh = make(chan struct{}, 1)
+				outW, _ := waiter.NewChannelEntry(outCh)
+				outFile.EventRegister(&outW, eventMaskWrite)
+				defer outFile.EventUnregister(&outW)
+				continue // Need to refresh readiness.
+			}
+			if err := t.Block(outCh); err != nil {
+				return 0, nil, err
+			}
+		}
+	}
+}
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2.go b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
index a332d01bd..083fdcf82 100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
@@ -134,8 +134,8 @@ func Override() {
 	s.Table[269] = syscalls.Supported("faccessat", Faccessat)
 	s.Table[270] = syscalls.Supported("pselect", Pselect)
 	s.Table[271] = syscalls.Supported("ppoll", Ppoll)
-	delete(s.Table, 275) // splice
-	delete(s.Table, 276) // tee
+	s.Table[275] = syscalls.Supported("splice", Splice)
+	s.Table[276] = syscalls.Supported("tee", Tee)
 	s.Table[277] = syscalls.Supported("sync_file_range", SyncFileRange)
 	s.Table[280] = syscalls.Supported("utimensat", Utimensat)
 	s.Table[281] = syscalls.Supported("epoll_pwait", EpollPwait)