Implement FUSE_CREATE

FUSE_CREATE is called when issuing creat(2) or open(2) with O_CREAT. It
creates a new file on the FUSE filesystem.

Fixes #3825

5 files changed, 208 insertions, 1 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index ed40df564..adc04dbcc 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -445,6 +445,48 @@ type FUSEReleaseIn struct {
 	LockOwner uint64
 }
 
+// FUSECreateMeta contains all the static fields of FUSECreateIn,
+// which is used for FUSE_CREATE.
+//
+// +marshal
+type FUSECreateMeta struct {
+	// Flags of the creating file.
+	Flags uint32
+
+	// Mode is the mode of the creating file.
+	Mode uint32
+
+	// Umask is the current file mode creation mask.
+	Umask uint32
+	_     uint32
+}
+
+// FUSECreateIn contains all the arguments sent by the kernel to the daemon, to
+// atomically create and open a new regular file.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSECreateIn struct {
+	marshal.StubMarshallable
+
+	// CreateMeta contains mode, rdev and umash field for FUSE_MKNODS.
+	CreateMeta FUSECreateMeta
+
+	// Name is the name of the node to create.
+	Name string
+}
+
+// MarshalBytes serializes r.CreateMeta and r.Name to the dst buffer.
+func (r *FUSECreateIn) MarshalBytes(buf []byte) {
+	r.CreateMeta.MarshalBytes(buf[:r.CreateMeta.SizeBytes()])
+	copy(buf[r.CreateMeta.SizeBytes():], r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSECreateIn.
+// 1 extra byte for null-terminated string.
+func (r *FUSECreateIn) SizeBytes() int {
+	return r.CreateMeta.SizeBytes() + len(r.Name) + 1
+}
+
 // FUSEMknodMeta contains all the static fields of FUSEMknodIn,
 // which is used for FUSE_MKNOD.
 //
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index e1bbb4b52..cfae9ed0d 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -392,6 +392,24 @@ func (inode) Valid(ctx context.Context) bool {
 	return true
 }
 
+// NewFile implements kernfs.Inode.NewFile.
+func (i *inode) NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (*vfs.Dentry, error) {
+	kernelTask := kernel.TaskFromContext(ctx)
+	if kernelTask == nil {
+		log.Warningf("fusefs.Inode.NewFile: couldn't get kernel task from context", i.NodeID)
+		return nil, syserror.EINVAL
+	}
+	in := linux.FUSECreateIn{
+		CreateMeta: linux.FUSECreateMeta{
+			Flags: opts.Flags,
+			Mode:  uint32(opts.Mode) | linux.S_IFREG,
+			Umask: uint32(kernelTask.FSContext().Umask()),
+		},
+		Name: name,
+	}
+	return i.newEntry(ctx, name, linux.S_IFREG, linux.FUSE_CREATE, &in)
+}
+
 // NewNode implements kernfs.Inode.NewNode.
 func (i *inode) NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (*vfs.Dentry, error) {
 	in := linux.FUSEMknodIn{
diff --git a/test/fuse/BUILD b/test/fuse/BUILD
index 02498b3a1..1a6b5b516 100644
--- a/test/fuse/BUILD
+++ b/test/fuse/BUILD
@@ -52,6 +52,10 @@ syscall_test(
     test = "//test/fuse/linux:readdir_test",
 )
 
+syscall_test(
+    fuse = "True",
+    test = "//test/fuse/linux:create_test",
+)
 
 syscall_test(
     size = "large",
diff --git a/test/fuse/linux/BUILD b/test/fuse/linux/BUILD
index 23c9fba31..2bb956af9 100644
--- a/test/fuse/linux/BUILD
+++ b/test/fuse/linux/BUILD
@@ -152,4 +152,19 @@ cc_binary(
         "//test/util:test_main",
         "//test/util:test_util",
     ],
-)
\ No newline at end of file
+)
+
+cc_binary(
+    name = "create_test",
+    testonly = 1,
+    srcs = ["create_test.cc"],
+    deps = [
+        gtest,
+        ":fuse_base",
+        "//test/util:fs_util",
+        "//test/util:fuse_util",
+        "//test/util:temp_umask",
+        "//test/util:test_main",
+        "//test/util:test_util",
+    ],
+)
diff --git a/test/fuse/linux/create_test.cc b/test/fuse/linux/create_test.cc
new file mode 100644
index 000000000..9a0219a58
--- /dev/null
+++ b/test/fuse/linux/create_test.cc
@@ -0,0 +1,128 @@
+// 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/stat.h>
+#include <sys/statfs.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "gtest/gtest.h"
+#include "test/fuse/linux/fuse_base.h"
+#include "test/util/fs_util.h"
+#include "test/util/fuse_util.h"
+#include "test/util/temp_umask.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+class CreateTest : public FuseTest {
+ protected:
+  const std::string test_file_name_ = "test_file";
+  const mode_t mode = S_IFREG | S_IRWXU | S_IRWXG | S_IRWXO;
+};
+
+TEST_F(CreateTest, CreateFile) {
+  const std::string test_file_path =
+      JoinPath(mount_point_.path().c_str(), test_file_name_);
+
+  // Ensure the file doesn't exist.
+  struct fuse_out_header out_header = {
+      .len = sizeof(struct fuse_out_header),
+      .error = -ENOENT,
+  };
+  auto iov_out = FuseGenerateIovecs(out_header);
+  SetServerResponse(FUSE_LOOKUP, iov_out);
+
+  // creat(2) is equal to open(2) with open_flags O_CREAT | O_WRONLY | O_TRUNC.
+  const mode_t new_mask = S_IWGRP | S_IWOTH;
+  const int open_flags = O_CREAT | O_WRONLY | O_TRUNC;
+  out_header.error = 0;
+  out_header.len = sizeof(struct fuse_out_header) +
+                   sizeof(struct fuse_entry_out) + sizeof(struct fuse_open_out);
+  struct fuse_entry_out entry_payload = DefaultEntryOut(mode & ~new_mask, 2);
+  struct fuse_open_out out_payload = {
+      .fh = 1,
+      .open_flags = open_flags,
+  };
+  iov_out = FuseGenerateIovecs(out_header, entry_payload, out_payload);
+  SetServerResponse(FUSE_CREATE, iov_out);
+
+  // kernfs generates a successive FUSE_OPEN after the file is created. Linux's
+  // fuse kernel module will not send this FUSE_OPEN after creat(2).
+  out_header.len =
+      sizeof(struct fuse_out_header) + sizeof(struct fuse_open_out);
+  iov_out = FuseGenerateIovecs(out_header, out_payload);
+  SetServerResponse(FUSE_OPEN, iov_out);
+
+  int fd;
+  TempUmask mask(new_mask);
+  EXPECT_THAT(fd = creat(test_file_path.c_str(), mode), SyscallSucceeds());
+  EXPECT_THAT(fcntl(fd, F_GETFL),
+              SyscallSucceedsWithValue(open_flags & O_ACCMODE));
+
+  struct fuse_in_header in_header;
+  struct fuse_create_in in_payload;
+  std::vector<char> name(test_file_name_.size() + 1);
+  auto iov_in = FuseGenerateIovecs(in_header, in_payload, name);
+
+  // Skip the request of FUSE_LOOKUP.
+  SkipServerActualRequest();
+
+  // Get the first FUSE_CREATE.
+  GetServerActualRequest(iov_in);
+  EXPECT_EQ(in_header.len, sizeof(in_header) + sizeof(in_payload) +
+                               test_file_name_.size() + 1);
+  EXPECT_EQ(in_header.opcode, FUSE_CREATE);
+  EXPECT_EQ(in_payload.flags, open_flags);
+  EXPECT_EQ(in_payload.mode, mode & ~new_mask);
+  EXPECT_EQ(in_payload.umask, new_mask);
+  EXPECT_EQ(std::string(name.data()), test_file_name_);
+
+  // Get the successive FUSE_OPEN.
+  struct fuse_open_in in_payload_open;
+  iov_in = FuseGenerateIovecs(in_header, in_payload_open);
+  GetServerActualRequest(iov_in);
+  EXPECT_EQ(in_header.len, sizeof(in_header) + sizeof(in_payload_open));
+  EXPECT_EQ(in_header.opcode, FUSE_OPEN);
+  EXPECT_EQ(in_payload_open.flags, open_flags & O_ACCMODE);
+
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+  // Skip the FUSE_RELEASE.
+  SkipServerActualRequest();
+}
+
+TEST_F(CreateTest, CreateFileAlreadyExists) {
+  const std::string test_file_path =
+      JoinPath(mount_point_.path().c_str(), test_file_name_);
+
+  const int open_flags = O_CREAT | O_EXCL;
+
+  SetServerInodeLookup(test_file_name_);
+
+  EXPECT_THAT(open(test_file_path.c_str(), mode, open_flags),
+              SyscallFailsWithErrno(EEXIST));
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor