os: add Root.Chmod

For #67002

Change-Id: Id6c3a2096bd10f5f5f6921a0441dc6d9e6cdeb3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/645718
Commit-Queue: Damien Neil <dneil@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>

13 files changed, 100 insertions, 4 deletions

diff --git a/src/internal/syscall/unix/asm_darwin.s b/src/internal/syscall/unix/asm_darwin.s
index b96eb1e807..de6e01ee4a 100644
--- a/src/internal/syscall/unix/asm_darwin.s
+++ b/src/internal/syscall/unix/asm_darwin.s
@@ -25,3 +25,4 @@ TEXT ·libc_sysconf_trampoline(SB),NOSPLIT,$0-0; JMP libc_sysconf(SB)
 TEXT ·libc_faccessat_trampoline(SB),NOSPLIT,$0-0; JMP libc_faccessat(SB)
 TEXT ·libc_readlinkat_trampoline(SB),NOSPLIT,$0-0; JMP libc_readlinkat(SB)
 TEXT ·libc_mkdirat_trampoline(SB),NOSPLIT,$0-0; JMP libc_mkdirat(SB)
+TEXT ·libc_fchmodat_trampoline(SB),NOSPLIT,$0-0; JMP libc_fchmodat(SB)
diff --git a/src/internal/syscall/unix/asm_openbsd.s b/src/internal/syscall/unix/asm_openbsd.s
index 90f6831e4e..306ef4664d 100644
--- a/src/internal/syscall/unix/asm_openbsd.s
+++ b/src/internal/syscall/unix/asm_openbsd.s
@@ -14,3 +14,5 @@ TEXT ·libc_readlinkat_trampoline(SB),NOSPLIT,$0-0
         JMP	libc_readlinkat(SB)
 TEXT ·libc_mkdirat_trampoline(SB),NOSPLIT,$0-0
         JMP	libc_mkdirat(SB)
+TEXT ·libc_fchmodat_trampoline(SB),NOSPLIT,$0-0
+        JMP	libc_fchmodat(SB)
diff --git a/src/internal/syscall/unix/at.go b/src/internal/syscall/unix/at.go
index 27a798e046..2a29dd6a5a 100644
--- a/src/internal/syscall/unix/at.go
+++ b/src/internal/syscall/unix/at.go
@@ -79,3 +79,20 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	}
 	return nil
 }
+
+func Fchmodat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall.Syscall6(fchmodatTrap,
+		uintptr(dirfd),
+		uintptr(unsafe.Pointer(p)),
+		uintptr(mode),
+		uintptr(flags),
+		0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
diff --git a/src/internal/syscall/unix/at_darwin.go b/src/internal/syscall/unix/at_darwin.go
index dbcae5a788..759b0943f5 100644
--- a/src/internal/syscall/unix/at_darwin.go
+++ b/src/internal/syscall/unix/at_darwin.go
@@ -58,3 +58,25 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	}
 	return nil
 }
+
+func libc_fchmodat_trampoline()
+
+//go:cgo_import_dynamic libc_fchmodat fchmodat "/usr/lib/libSystem.B.dylib"
+
+func Fchmodat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall_syscall6(abi.FuncPCABI0(libc_fchmodat_trampoline),
+		uintptr(dirfd),
+		uintptr(unsafe.Pointer(p)),
+		uintptr(mode),
+		uintptr(flags),
+		0,
+		0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
diff --git a/src/internal/syscall/unix/at_libc.go b/src/internal/syscall/unix/at_libc.go
index faf38be602..f88e09d31d 100644
--- a/src/internal/syscall/unix/at_libc.go
+++ b/src/internal/syscall/unix/at_libc.go
@@ -16,13 +16,15 @@ import (
 //go:linkname procUnlinkat libc_unlinkat
 //go:linkname procReadlinkat libc_readlinkat
 //go:linkname procMkdirat libc_mkdirat
+//go:linkname procFchmodat libc_fchmodat
 
 var (
 	procFstatat,
 	procOpenat,
 	procUnlinkat,
 	procReadlinkat,
-	procMkdirat uintptr
+	procMkdirat,
+	procFchmodat uintptr
 )
 
 func Unlinkat(dirfd int, path string, flags int) error {
@@ -107,3 +109,20 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	}
 	return nil
 }
+
+func Fchmodat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall6(uintptr(unsafe.Pointer(&procFchmodat)), 4,
+		uintptr(dirfd),
+		uintptr(unsafe.Pointer(p)),
+		uintptr(mode),
+		uintptr(flags),
+		0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
diff --git a/src/internal/syscall/unix/at_openbsd.go b/src/internal/syscall/unix/at_openbsd.go
index 69463e00b9..26ca70322b 100644
--- a/src/internal/syscall/unix/at_openbsd.go
+++ b/src/internal/syscall/unix/at_openbsd.go
@@ -49,3 +49,25 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	}
 	return nil
 }
+
+//go:cgo_import_dynamic libc_fchmodat fchmodat "libc.so"
+
+func libc_fchmodat_trampoline()
+
+func Fchmodat(dirfd int, path string, mode uint32, flags int) error {
+	p, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall_syscall6(abi.FuncPCABI0(libc_fchmodat_trampoline),
+		uintptr(dirfd),
+		uintptr(unsafe.Pointer(p)),
+		uintptr(mode),
+		uintptr(flags),
+		0,
+		0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}
diff --git a/src/internal/syscall/unix/at_sysnum_dragonfly.go b/src/internal/syscall/unix/at_sysnum_dragonfly.go
index d0ba12a78a..84c60c47b8 100644
--- a/src/internal/syscall/unix/at_sysnum_dragonfly.go
+++ b/src/internal/syscall/unix/at_sysnum_dragonfly.go
@@ -12,6 +12,7 @@ const (
 	fstatatTrap    uintptr = syscall.SYS_FSTATAT
 	readlinkatTrap uintptr = syscall.SYS_READLINKAT
 	mkdiratTrap    uintptr = syscall.SYS_MKDIRAT
+	fchmodatTrap   uintptr = syscall.SYS_FCHMODAT
 
 	AT_EACCESS          = 0x4
 	AT_FDCWD            = 0xfffafdcd
diff --git a/src/internal/syscall/unix/at_sysnum_freebsd.go b/src/internal/syscall/unix/at_sysnum_freebsd.go
index 0f34722432..22ff4e7e89 100644
--- a/src/internal/syscall/unix/at_sysnum_freebsd.go
+++ b/src/internal/syscall/unix/at_sysnum_freebsd.go
@@ -19,4 +19,5 @@ const (
 	posixFallocateTrap uintptr = syscall.SYS_POSIX_FALLOCATE
 	readlinkatTrap     uintptr = syscall.SYS_READLINKAT
 	mkdiratTrap        uintptr = syscall.SYS_MKDIRAT
+	fchmodatTrap       uintptr = syscall.SYS_FCHMODAT
 )
diff --git a/src/internal/syscall/unix/at_sysnum_linux.go b/src/internal/syscall/unix/at_sysnum_linux.go
index 2885c7c681..8fba319cab 100644
--- a/src/internal/syscall/unix/at_sysnum_linux.go
+++ b/src/internal/syscall/unix/at_sysnum_linux.go
@@ -11,6 +11,7 @@ const (
 	openatTrap     uintptr = syscall.SYS_OPENAT
 	readlinkatTrap uintptr = syscall.SYS_READLINKAT
 	mkdiratTrap    uintptr = syscall.SYS_MKDIRAT
+	fchmodatTrap   uintptr = syscall.SYS_FCHMODAT
 )
 
 const (
diff --git a/src/internal/syscall/unix/at_sysnum_netbsd.go b/src/internal/syscall/unix/at_sysnum_netbsd.go
index 820b977436..f2b7a4f9eb 100644
--- a/src/internal/syscall/unix/at_sysnum_netbsd.go
+++ b/src/internal/syscall/unix/at_sysnum_netbsd.go
@@ -12,6 +12,7 @@ const (
 	fstatatTrap    uintptr = syscall.SYS_FSTATAT
 	readlinkatTrap uintptr = syscall.SYS_READLINKAT
 	mkdiratTrap    uintptr = syscall.SYS_MKDIRAT
+	fchmodatTrap   uintptr = syscall.SYS_FCHMODAT
 )
 
 const (
diff --git a/src/internal/syscall/unix/at_wasip1.go b/src/internal/syscall/unix/at_wasip1.go
index cd0cb4b7e4..7289317110 100644
--- a/src/internal/syscall/unix/at_wasip1.go
+++ b/src/internal/syscall/unix/at_wasip1.go
@@ -101,6 +101,11 @@ func Mkdirat(dirfd int, path string, mode uint32) error {
 	))
 }
 
+func Fchmodat(dirfd int, path string, mode uint32, flags int) error {
+	// WASI preview 1 doesn't support changing file modes.
+	return syscall.ENOSYS
+}
+
 //go:wasmimport wasi_snapshot_preview1 path_create_directory
 //go:noescape
 func path_create_directory(fd int32, path *byte, pathLen size) syscall.Errno
diff --git a/src/internal/syscall/windows/at_windows.go b/src/internal/syscall/windows/at_windows.go
index 18429773c0..19bcc0dbac 100644
--- a/src/internal/syscall/windows/at_windows.go
+++ b/src/internal/syscall/windows/at_windows.go
@@ -20,9 +20,10 @@ const (
 	O_DIRECTORY    = 0x100000   // target must be a directory
 	O_NOFOLLOW_ANY = 0x20000000 // disallow symlinks anywhere in the path
 	O_OPEN_REPARSE = 0x40000000 // FILE_OPEN_REPARSE_POINT, used by Lstat
+	O_WRITE_ATTRS  = 0x80000000 // FILE_WRITE_ATTRIBUTES, used by Chmod
 )
 
-func Openat(dirfd syscall.Handle, name string, flag int, perm uint32) (_ syscall.Handle, e1 error) {
+func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ syscall.Handle, e1 error) {
 	if len(name) == 0 {
 		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
 	}
@@ -61,6 +62,9 @@ func Openat(dirfd syscall.Handle, name string, flag int, perm uint32) (_ syscall
 	if flag&syscall.O_SYNC != 0 {
 		options |= FILE_WRITE_THROUGH
 	}
+	if flag&O_WRITE_ATTRS != 0 {
+		access |= FILE_WRITE_ATTRIBUTES
+	}
 	// Allow File.Stat.
 	access |= STANDARD_RIGHTS_READ | FILE_READ_ATTRIBUTES | FILE_READ_EA
 
@@ -129,7 +133,7 @@ func Openat(dirfd syscall.Handle, name string, flag int, perm uint32) (_ syscall
 }
 
 // ntCreateFileError maps error returns from NTCreateFile to user-visible errors.
-func ntCreateFileError(err error, flag int) error {
+func ntCreateFileError(err error, flag uint64) error {
 	s, ok := err.(NTStatus)
 	if !ok {
 		// Shouldn't really be possible, NtCreateFile always returns NTStatus.
diff --git a/src/internal/syscall/windows/at_windows_test.go b/src/internal/syscall/windows/at_windows_test.go
index 7da9ecf07a..daeb4fcde3 100644
--- a/src/internal/syscall/windows/at_windows_test.go
+++ b/src/internal/syscall/windows/at_windows_test.go
@@ -46,7 +46,7 @@ func TestOpen(t *testing.T) {
 			continue
 		}
 		base := filepath.Base(tt.path)
-		h, err := windows.Openat(dirfd, base, tt.flag, 0o660)
+		h, err := windows.Openat(dirfd, base, uint64(tt.flag), 0o660)
 		syscall.CloseHandle(dirfd)
 		if err == nil {
 			syscall.CloseHandle(h)