fusefrontend: run acl Setxattr in user context

The result of setting an acl depends on who runs the
operation!

Fixes fuse-xfstests generic/375
(see https://github.com/rfjakob/fuse-xfstests/wiki/results_2021-05-19)

1 files changed, 20 insertions, 0 deletions

diff --git a/internal/syscallcompat/sys_linux.go b/internal/syscallcompat/sys_linux.go
index 36ce7d5..45c18d2 100644
--- a/internal/syscallcompat/sys_linux.go
+++ b/internal/syscallcompat/sys_linux.go
@@ -130,6 +130,9 @@ func asUser(f func() (int, error), context *fuse.Context) (int, error) {
 //
 // It switches the current thread to the new user, performs the syscall,
 // and switches back.
+//
+// If `context` is nil, this function behaves like ordinary Openat (no
+// user switching).
 func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
 	f := func() (int, error) {
 		return Openat(dirfd, path, flags, mode)
@@ -143,6 +146,7 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
 }
 
 // MknodatUser runs the Mknodat syscall in the context of a different user.
+// If `context` is nil, this function behaves like ordinary Mknodat.
 //
 // See OpenatUser() for how this works.
 func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
@@ -195,6 +199,7 @@ func FchmodatNofollow(dirfd int, path string, mode uint32) (err error) {
 }
 
 // SymlinkatUser runs the Symlinkat syscall in the context of a different user.
+// If `context` is nil, this function behaves like ordinary Symlinkat.
 //
 // See OpenatUser() for how this works.
 func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
@@ -207,6 +212,7 @@ func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.C
 }
 
 // MkdiratUser runs the Mkdirat syscall in the context of a different user.
+// If `context` is nil, this function behaves like ordinary Mkdirat.
 //
 // See OpenatUser() for how this works.
 func MkdiratUser(dirfd int, path string, mode uint32, context *fuse.Context) (err error) {
@@ -218,6 +224,20 @@ func MkdiratUser(dirfd int, path string, mode uint32, context *fuse.Context) (er
 	return err
 }
 
+// LsetxattrUser runs the Lsetxattr syscall in the context of a different user.
+// This is useful when setting ACLs, as the result depends on the user running
+// the operation (see fuse-xfstests generic/375).
+//
+// If `context` is nil, this function behaves like ordinary Lsetxattr.
+func LsetxattrUser(path string, attr string, data []byte, flags int, context *fuse.Context) (err error) {
+	f := func() (int, error) {
+		err := unix.Lsetxattr(path, attr, data, flags)
+		return -1, err
+	}
+	_, err = asUser(f, context)
+	return err
+}
+
 func timesToTimespec(a *time.Time, m *time.Time) []unix.Timespec {
 	ts := make([]unix.Timespec, 2)
 	ts[0] = unix.Timespec(fuse.UtimeToTimespec(a))