Implement FUSE_UNLINK

Fixes #3696

pkg/abi/linux/fuse.go

@@ -846,3 +846,26 @@ type FUSESetAttrIn struct {
 
 	_ uint32
 }
+
+// FUSEUnlinkIn is the request sent by the kernel to the daemon
+// when trying to unlink a node.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSEUnlinkIn struct {
+	marshal.StubMarshallable
+
+	// Name of the node to unlink.
+	Name string
+}
+
+// MarshalBytes serializes r.name to the dst buffer, which should
+// have size len(r.Name) + 1 and last byte set to 0.
+func (r *FUSEUnlinkIn) MarshalBytes(buf []byte) {
+	copy(buf, r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSEUnlinkIn.
+// 1 extra byte for null-terminated Name string.
+func (r *FUSEUnlinkIn) SizeBytes() int {
+	return len(r.Name) + 1
+}

pkg/sentry/fsimpl/fuse/fusefs.go

@@ -455,6 +455,29 @@ func (i *inode) NewSymlink(ctx context.Context, name, target string) (*vfs.Dentr
 	return i.newEntry(ctx, name, linux.S_IFLNK, linux.FUSE_SYMLINK, &in)
 }
 
+// Unlink implements kernfs.Inode.Unlink.
+func (i *inode) Unlink(ctx context.Context, name string, child *vfs.Dentry) error {
+	kernelTask := kernel.TaskFromContext(ctx)
+	if kernelTask == nil {
+		log.Warningf("fusefs.Inode.newEntry: couldn't get kernel task from context", i.NodeID)
+		return syserror.EINVAL
+	}
+	in := linux.FUSEUnlinkIn{Name: name}
+	req, err := i.fs.conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(kernelTask.ThreadID()), i.NodeID, linux.FUSE_UNLINK, &in)
+	if err != nil {
+		return err
+	}
+	res, err := i.fs.conn.Call(kernelTask, req)
+	if err != nil {
+		return err
+	}
+	// only return error, discard res.
+	if err := res.Error(); err != nil {
+		return err
+	}
+	return i.dentry.RemoveChildLocked(name, child)
+}
+
 // NewDir implements kernfs.Inode.NewDir.
 func (i *inode) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error) {
 	in := linux.FUSEMkdirIn{

pkg/sentry/fsimpl/kernfs/filesystem.go

@@ -770,6 +770,10 @@ func (fs *Filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, targ
 func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error {
 	fs.mu.Lock()
 	defer fs.mu.Unlock()
+
+	// Store the name before walkExistingLocked as rp will be advanced past the
+	// name in the following call.
+	name := rp.Component()
 	vfsd, _, err := fs.walkExistingLocked(ctx, rp)
 	fs.processDeferredDecRefsLocked(ctx)
 	if err != nil {
@@ -795,7 +799,7 @@ func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
 		return err
 	}
-	if err := parentDentry.inode.Unlink(ctx, rp.Component(), vfsd); err != nil {
+	if err := parentDentry.inode.Unlink(ctx, name, vfsd); err != nil {
 		virtfs.AbortDeleteDentry(vfsd)
 		return err
 	}

pkg/sentry/fsimpl/kernfs/kernfs.go

@@ -60,6 +60,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // Filesystem mostly implements vfs.FilesystemImpl for a generic in-memory
@@ -267,6 +268,36 @@ func (d *Dentry) InsertChildLocked(name string, child *Dentry) {
 	d.children[name] = child
 }
 
+// RemoveChild removes child from the vfs dentry cache. This does not update the
+// directory inode or modify the inode to be unlinked. So calling this on its own
+// isn't sufficient to remove a child from a directory.
+//
+// Precondition: d must represent a directory inode.
+func (d *Dentry) RemoveChild(name string, child *vfs.Dentry) error {
+	d.dirMu.Lock()
+	defer d.dirMu.Unlock()
+	return d.RemoveChildLocked(name, child)
+}
+
+// RemoveChildLocked is equivalent to RemoveChild, with additional
+// preconditions.
+//
+// Precondition: d.dirMu must be locked.
+func (d *Dentry) RemoveChildLocked(name string, child *vfs.Dentry) error {
+	if !d.isDir() {
+		panic(fmt.Sprintf("RemoveChild called on non-directory Dentry: %+v.", d))
+	}
+	c, ok := d.children[name]
+	if !ok {
+		return syserror.ENOENT
+	}
+	if &c.vfsd != child {
+		panic(fmt.Sprintf("Dentry hashed into inode doesn't match what vfs thinks! Child: %+v, vfs: %+v", c, child))
+	}
+	delete(d.children, name)
+	return nil
+}
+
 // Inode returns the dentry's inode.
 func (d *Dentry) Inode() Inode {
 	return d.inode

test/fuse/BUILD

@@ -62,6 +62,11 @@ syscall_test(
     test = "//test/fuse/linux:create_test",
 )
 
+syscall_test(
+    fuse = "True",
+    test = "//test/fuse/linux:unlink_test",
+)
+
 syscall_test(
     fuse = "True",
     test = "//test/fuse/linux:setstat_test",

test/fuse/linux/BUILD

@@ -214,3 +214,17 @@ cc_binary(
         "//test/util:test_util",
     ],
 )
+
+cc_binary(
+    name = "unlink_test",
+    testonly = 1,
+    srcs = ["unlink_test.cc"],
+    deps = [
+        gtest,
+        ":fuse_base",
+        "//test/util:fuse_util",
+        "//test/util:temp_umask",
+        "//test/util:test_main",
+        "//test/util:test_util",
+    ],
+)

test/fuse/linux/unlink_test.cc

@@ -0,0 +1,83 @@
+// 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.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/fuse.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/statfs.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "test/fuse/linux/fuse_base.h"
+#include "test/util/fuse_util.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+class UnlinkTest : public FuseTest {
+ protected:
+  const std::string test_file_ = "test_file";
+};
+
+TEST_F(UnlinkTest, RegularFile) {
+  const std::string test_file_path =
+      JoinPath(mount_point_.path().c_str(), test_file_);
+  SetServerInodeLookup(test_file_, S_IFREG | S_IRWXU | S_IRWXG | S_IRWXO);
+
+  struct fuse_out_header out_header = {
+      .len = sizeof(struct fuse_out_header),
+  };
+  auto iov_out = FuseGenerateIovecs(out_header);
+  SetServerResponse(FUSE_UNLINK, iov_out);
+
+  ASSERT_THAT(unlink(test_file_path.c_str()), SyscallSucceeds());
+  struct fuse_in_header in_header;
+  std::vector<char> unlinked_file(test_file_.length() + 1);
+  auto iov_in = FuseGenerateIovecs(in_header, unlinked_file);
+  GetServerActualRequest(iov_in);
+
+  EXPECT_EQ(in_header.len, sizeof(in_header) + test_file_.length() + 1);
+  EXPECT_EQ(in_header.opcode, FUSE_UNLINK);
+  EXPECT_EQ(std::string(unlinked_file.data()), test_file_);
+}
+
+TEST_F(UnlinkTest, NoFile) {
+  const std::string test_file_path =
+      JoinPath(mount_point_.path().c_str(), test_file_);
+  SetServerInodeLookup(test_file_, S_IFREG | S_IRWXU | S_IRWXG | S_IRWXO);
+
+  struct fuse_out_header out_header = {
+      .len = sizeof(struct fuse_out_header),
+      .error = -ENOENT,
+  };
+  auto iov_out = FuseGenerateIovecs(out_header);
+  SetServerResponse(FUSE_UNLINK, iov_out);
+
+  ASSERT_THAT(unlink(test_file_path.c_str()), SyscallFailsWithErrno(ENOENT));
+  SkipServerActualRequest();
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor