Port extended attributes to VFS2.

As in VFS1, we only support the user.* namespace. Plumbing is added to tmpfs
and goferfs.
Note that because of the slightly different order of checks between VFS2 and
Linux, one of the xattr tests needs to be relaxed slightly.

Fixes #2363.

PiperOrigin-RevId: 305985121

2 files changed, 117 insertions, 0 deletions

diff --git a/pkg/sentry/vfs/memxattr/BUILD b/pkg/sentry/vfs/memxattr/BUILD
new file mode 100644
index 000000000..d8c4d27b9
--- /dev/null
+++ b/pkg/sentry/vfs/memxattr/BUILD
@@ -0,0 +1,15 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "memxattr",
+    srcs = ["xattr.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/sentry/vfs",
+        "//pkg/sync",
+        "//pkg/syserror",
+    ],
+)
diff --git a/pkg/sentry/vfs/memxattr/xattr.go b/pkg/sentry/vfs/memxattr/xattr.go
new file mode 100644
index 000000000..cc1e7d764
--- /dev/null
+++ b/pkg/sentry/vfs/memxattr/xattr.go
@@ -0,0 +1,102 @@
+// 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 memxattr provides a default, in-memory extended attribute
+// implementation.
+package memxattr
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// SimpleExtendedAttributes implements extended attributes using a map of
+// names to values.
+//
+// +stateify savable
+type SimpleExtendedAttributes struct {
+	// mu protects the below fields.
+	mu     sync.RWMutex `state:"nosave"`
+	xattrs map[string]string
+}
+
+// Getxattr returns the value at 'name'.
+func (x *SimpleExtendedAttributes) Getxattr(opts *vfs.GetxattrOptions) (string, error) {
+	x.mu.RLock()
+	value, ok := x.xattrs[opts.Name]
+	x.mu.RUnlock()
+	if !ok {
+		return "", syserror.ENODATA
+	}
+	// Check that the size of the buffer provided in getxattr(2) is large enough
+	// to contain the value.
+	if opts.Size != 0 && uint64(len(value)) > opts.Size {
+		return "", syserror.ERANGE
+	}
+	return value, nil
+}
+
+// Setxattr sets 'value' at 'name'.
+func (x *SimpleExtendedAttributes) Setxattr(opts *vfs.SetxattrOptions) error {
+	x.mu.Lock()
+	defer x.mu.Unlock()
+	if x.xattrs == nil {
+		if opts.Flags&linux.XATTR_REPLACE != 0 {
+			return syserror.ENODATA
+		}
+		x.xattrs = make(map[string]string)
+	}
+
+	_, ok := x.xattrs[opts.Name]
+	if ok && opts.Flags&linux.XATTR_CREATE != 0 {
+		return syserror.EEXIST
+	}
+	if !ok && opts.Flags&linux.XATTR_REPLACE != 0 {
+		return syserror.ENODATA
+	}
+
+	x.xattrs[opts.Name] = opts.Value
+	return nil
+}
+
+// Listxattr returns all names in xattrs.
+func (x *SimpleExtendedAttributes) Listxattr(size uint64) ([]string, error) {
+	// Keep track of the size of the buffer needed in listxattr(2) for the list.
+	listSize := 0
+	x.mu.RLock()
+	names := make([]string, 0, len(x.xattrs))
+	for n := range x.xattrs {
+		names = append(names, n)
+		// Add one byte per null terminator.
+		listSize += len(n) + 1
+	}
+	x.mu.RUnlock()
+	if size != 0 && uint64(listSize) > size {
+		return nil, syserror.ERANGE
+	}
+	return names, nil
+}
+
+// Removexattr removes the xattr at 'name'.
+func (x *SimpleExtendedAttributes) Removexattr(name string) error {
+	x.mu.Lock()
+	defer x.mu.Unlock()
+	if _, ok := x.xattrs[name]; !ok {
+		return syserror.ENODATA
+	}
+	delete(x.xattrs, name)
+	return nil
+}