Fix ptsname() for big-endian architectures

pmorjan · pmorjan · commit dbd69c59b81e · 2018-02-19T09:06:48.000+01:00
On big-endian architectures unix.IoctlGetInt() leads to a wrong result
because a 32 bit value is stored into a 64 bit buffer. When dereferencing
the result is left shifted by 32. Without this patch ptsname() returns
a wrong path from the second pty onwards.
To protect syscalls against re-arranging by the GC the conversion from
unsafe.Pointer to uintptr must occur in the Syscall expression itself.
See the documentation of the unsafe package for details.

Signed-off-by: Peter Morjan &lt;peter.morjan@de.ibm.com&gt;
diff --git a/tc_linux.go b/tc_linux.go
@@ -13,25 +13,21 @@ const (
 	cmdTcSet = unix.TCSETS
 )
 
-func ioctl(fd, flag, data uintptr) error {
-	if _, _, err := unix.Syscall(unix.SYS_IOCTL, fd, flag, data); err != 0 {
-		return err
-	}
-	return nil
-}
-
 // unlockpt unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by f.
 // unlockpt should be called before opening the slave side of a pty.
 func unlockpt(f *os.File) error {
 	var u int32
-	return ioctl(f.Fd(), unix.TIOCSPTLCK, uintptr(unsafe.Pointer(&u)))
+	if _, _, err := unix.Syscall(unix.SYS_IOCTL, f.Fd(), unix.TIOCSPTLCK, uintptr(unsafe.Pointer(&u))); err != 0 {
+		return err
+	}
+	return nil
 }
 
 // ptsname retrieves the name of the first available pts for the given master.
 func ptsname(f *os.File) (string, error) {
-	n, err := unix.IoctlGetInt(int(f.Fd()), unix.TIOCGPTN)
-	if err != nil {
+	var u uint32
+	if _, _, err := unix.Syscall(unix.SYS_IOCTL, f.Fd(), unix.TIOCGPTN, uintptr(unsafe.Pointer(&u))); err != 0 {
 		return "", err
 	}
-	return fmt.Sprintf("/dev/pts/%d", n), nil
+	return fmt.Sprintf("/dev/pts/%d", u), nil
 }
