From 5055f39bd534b1f13257f95ffdc28575b9b2e3ed Mon Sep 17 00:00:00 2001
From: Sebastian Lackner
Date: Sat, 5 Jan 2019 04:33:50 +0100
Subject: fusefrontend: Allow to set/remove xattr on directory without read
 permission.

Setting/removing extended attributes on directories was partially fixed with
commit eff35e60b63331e3e10f921792baa10b236a721d. However, on most file systems
it is also possible to do these operations without read access (see tests).

Since we cannot open a write-access fd to a directory, we have to use the
/proc/self/fd trick (already used for ListXAttr) for the other operations aswell.
For simplicity, let's separate the Linux and Darwin code again (basically revert
commit f320b76fd189a363a34bffe981aa67ab97df3362), and always use the
/proc/self/fd trick on Linux. On Darwin we use the best-effort approach with
openBackingFile() as a fallback.

More discussion about the available options is available in
https://github.com/rfjakob/gocryptfs/issues/308.
---
 internal/fusefrontend/xattr_linux.go | 62 ++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

(limited to 'internal/fusefrontend/xattr_linux.go')

diff --git a/internal/fusefrontend/xattr_linux.go b/internal/fusefrontend/xattr_linux.go
index fd3b7e5..3a64412 100644
--- a/internal/fusefrontend/xattr_linux.go
+++ b/internal/fusefrontend/xattr_linux.go
@@ -4,7 +4,15 @@
 package fusefrontend
 
 import (
+	"fmt"
 	"strings"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 )
 
 // Only allow the "user" namespace, block "trusted" and "security", as
@@ -19,3 +27,57 @@ func disallowedXAttrName(attr string) bool {
 func filterXattrSetFlags(flags int) int {
 	return flags
 }
+
+func (fs *FS) getXAttr(relPath string, cAttr string, context *fuse.Context) ([]byte, fuse.Status) {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	cData, err := syscallcompat.Lgetxattr(procPath, cAttr)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return cData, fuse.OK
+}
+
+func (fs *FS) setXAttr(relPath string, cAttr string, cData []byte, flags int, context *fuse.Context) fuse.Status {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	err = unix.Lsetxattr(procPath, cAttr, cData, flags)
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) removeXAttr(relPath string, cAttr string, context *fuse.Context) fuse.Status {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	err = unix.Lremovexattr(procPath, cAttr)
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) listXAttr(relPath string, context *fuse.Context) ([]string, fuse.Status) {
+	dirfd, cName, err := fs.openBackingDir(relPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	defer syscall.Close(dirfd)
+
+	procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
+	cNames, err := syscallcompat.Llistxattr(procPath)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return cNames, fuse.OK
+}
-- 
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