Implement checks for get/setxattr at the syscall layer.

Add checks for input arguments, file type, permissions, etc. that match
the Linux implementation. A call to get/setxattr that passes all the
checks will still currently return EOPNOTSUPP. Actual support will be
added in following commits.

Only allow user.* extended attributes for the time being.

PiperOrigin-RevId: 285835159

4 files changed, 174 insertions, 4 deletions

diff --git a/pkg/sentry/syscalls/linux/BUILD b/pkg/sentry/syscalls/linux/BUILD
index 4c0bf96e4..6766ba587 100644
--- a/pkg/sentry/syscalls/linux/BUILD
+++ b/pkg/sentry/syscalls/linux/BUILD
@@ -49,6 +49,7 @@ go_library(
         "sys_tls.go",
         "sys_utsname.go",
         "sys_write.go",
+        "sys_xattr.go",
         "timespec.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/syscalls/linux",
diff --git a/pkg/sentry/syscalls/linux/linux64_amd64.go b/pkg/sentry/syscalls/linux/linux64_amd64.go
index 797542d28..272ae9991 100644
--- a/pkg/sentry/syscalls/linux/linux64_amd64.go
+++ b/pkg/sentry/syscalls/linux/linux64_amd64.go
@@ -228,10 +228,10 @@ var AMD64 = &kernel.SyscallTable{
 		185: syscalls.Error("security", syserror.ENOSYS, "Not implemented in Linux.", nil),
 		186: syscalls.Supported("gettid", Gettid),
 		187: syscalls.Supported("readahead", Readahead),
-		188: syscalls.Error("setxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
+		188: syscalls.PartiallySupported("setxattr", Setxattr, "Only supported for tmpfs.", nil),
 		189: syscalls.Error("lsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		190: syscalls.Error("fsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
-		191: syscalls.ErrorWithEvent("getxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
+		191: syscalls.PartiallySupported("getxattr", Getxattr, "Only supported for tmpfs.", nil),
 		192: syscalls.ErrorWithEvent("lgetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		193: syscalls.ErrorWithEvent("fgetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		194: syscalls.ErrorWithEvent("listxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
diff --git a/pkg/sentry/syscalls/linux/linux64_arm64.go b/pkg/sentry/syscalls/linux/linux64_arm64.go
index 2bc7faff5..3b584eed9 100644
--- a/pkg/sentry/syscalls/linux/linux64_arm64.go
+++ b/pkg/sentry/syscalls/linux/linux64_arm64.go
@@ -41,10 +41,10 @@ var ARM64 = &kernel.SyscallTable{
 		2:   syscalls.PartiallySupported("io_submit", IoSubmit, "Generally supported with exceptions. User ring optimizations are not implemented.", []string{"gvisor.dev/issue/204"}),
 		3:   syscalls.PartiallySupported("io_cancel", IoCancel, "Generally supported with exceptions. User ring optimizations are not implemented.", []string{"gvisor.dev/issue/204"}),
 		4:   syscalls.PartiallySupported("io_getevents", IoGetevents, "Generally supported with exceptions. User ring optimizations are not implemented.", []string{"gvisor.dev/issue/204"}),
-		5:   syscalls.Error("setxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
+		5:   syscalls.PartiallySupported("setxattr", Setxattr, "Only supported for tmpfs.", nil),
 		6:   syscalls.Error("lsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		7:   syscalls.Error("fsetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
-		8:   syscalls.ErrorWithEvent("getxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
+		8:   syscalls.PartiallySupported("getxattr", Getxattr, "Only supported for tmpfs.", nil),
 		9:   syscalls.ErrorWithEvent("lgetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		10:  syscalls.ErrorWithEvent("fgetxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
 		11:  syscalls.ErrorWithEvent("listxattr", syserror.ENOTSUP, "Requires filesystem support.", nil),
diff --git a/pkg/sentry/syscalls/linux/sys_xattr.go b/pkg/sentry/syscalls/linux/sys_xattr.go
new file mode 100644
index 000000000..97d9a65ea
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/sys_xattr.go
@@ -0,0 +1,169 @@
+// Copyright 2019 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 linux
+
+import (
+	"strings"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// Getxattr implements linux syscall getxattr(2).
+func Getxattr(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	pathAddr := args[0].Pointer()
+	nameAddr := args[1].Pointer()
+	valueAddr := args[2].Pointer()
+	size := args[3].SizeT()
+
+	path, dirPath, err := copyInPath(t, pathAddr, false /* allowEmpty */)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	valueLen := 0
+	err = fileOpOn(t, linux.AT_FDCWD, path, true /* resolve */, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
+		value, err := getxattr(t, d, dirPath, nameAddr)
+		if err != nil {
+			return err
+		}
+
+		valueLen = len(value)
+		if size == 0 {
+			return nil
+		}
+		if size > linux.XATTR_SIZE_MAX {
+			size = linux.XATTR_SIZE_MAX
+		}
+		if valueLen > int(size) {
+			return syserror.ERANGE
+		}
+
+		_, err = t.CopyOutBytes(valueAddr, []byte(value))
+		return err
+	})
+	if err != nil {
+		return 0, nil, err
+	}
+	return uintptr(valueLen), nil, nil
+}
+
+// getxattr implements getxattr from the given *fs.Dirent.
+func getxattr(t *kernel.Task, d *fs.Dirent, dirPath bool, nameAddr usermem.Addr) (string, error) {
+	if dirPath && !fs.IsDir(d.Inode.StableAttr) {
+		return "", syserror.ENOTDIR
+	}
+
+	if err := checkXattrPermissions(t, d.Inode, fs.PermMask{Read: true}); err != nil {
+		return "", err
+	}
+
+	name, err := copyInXattrName(t, nameAddr)
+	if err != nil {
+		return "", err
+	}
+
+	if !strings.HasPrefix(name, linux.XATTR_USER_PREFIX) {
+		return "", syserror.EOPNOTSUPP
+	}
+
+	return d.Inode.Getxattr(name)
+}
+
+// Setxattr implements linux syscall setxattr(2).
+func Setxattr(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	pathAddr := args[0].Pointer()
+	nameAddr := args[1].Pointer()
+	valueAddr := args[2].Pointer()
+	size := args[3].SizeT()
+	flags := args[4].Uint()
+
+	path, dirPath, err := copyInPath(t, pathAddr, false /* allowEmpty */)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	if flags&^(linux.XATTR_CREATE|linux.XATTR_REPLACE) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	return 0, nil, fileOpOn(t, linux.AT_FDCWD, path, true /* resolve */, func(root *fs.Dirent, d *fs.Dirent, _ uint) error {
+		return setxattr(t, d, dirPath, nameAddr, valueAddr, size, flags)
+	})
+}
+
+// setxattr implements setxattr from the given *fs.Dirent.
+func setxattr(t *kernel.Task, d *fs.Dirent, dirPath bool, nameAddr, valueAddr usermem.Addr, size uint, flags uint32) error {
+	if dirPath && !fs.IsDir(d.Inode.StableAttr) {
+		return syserror.ENOTDIR
+	}
+
+	if err := checkXattrPermissions(t, d.Inode, fs.PermMask{Write: true}); err != nil {
+		return err
+	}
+
+	name, err := copyInXattrName(t, nameAddr)
+	if err != nil {
+		return err
+	}
+
+	if size > linux.XATTR_SIZE_MAX {
+		return syserror.E2BIG
+	}
+	buf := make([]byte, size)
+	if _, err = t.CopyInBytes(valueAddr, buf); err != nil {
+		return err
+	}
+	value := string(buf)
+
+	if !strings.HasPrefix(name, linux.XATTR_USER_PREFIX) {
+		return syserror.EOPNOTSUPP
+	}
+
+	return d.Inode.Setxattr(name, value)
+}
+
+func copyInXattrName(t *kernel.Task, nameAddr usermem.Addr) (string, error) {
+	name, err := t.CopyInString(nameAddr, linux.XATTR_NAME_MAX+1)
+	if err != nil {
+		if err == syserror.ENAMETOOLONG {
+			return "", syserror.ERANGE
+		}
+		return "", err
+	}
+	if len(name) == 0 {
+		return "", syserror.ERANGE
+	}
+	return name, nil
+}
+
+func checkXattrPermissions(t *kernel.Task, i *fs.Inode, perms fs.PermMask) error {
+	// Restrict xattrs to regular files and directories.
+	//
+	// In Linux, this restriction technically only applies to xattrs in the
+	// "user.*" namespace, but we don't allow any other xattr prefixes anyway.
+	if !fs.IsRegular(i.StableAttr) && !fs.IsDir(i.StableAttr) {
+		if perms.Write {
+			return syserror.EPERM
+		}
+		return syserror.ENODATA
+	}
+
+	return i.CheckPermission(t, perms)
+}