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
+}