syscall: fix wrong unsafe.Pointer alignment in syscall

Caught with:

	go test -a -short -gcflags=all=-d=checkptr log/syslog

and:

	grep -rE '\*\[([^2]|.{2,})\].*\)\(unsafe.Pointer' syscall

Updates #34972

Change-Id: Iafd199b3a34beb7cc3e88484bf2fbae45183f951
Reviewed-on: https://go-review.googlesource.com/c/go/+/201877
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/syscall/security_windows.go

@@ -157,13 +157,15 @@ func LookupSID(system, account string) (sid *SID, domain string, accType uint32,
 // String converts sid to a string format
 // suitable for display, storage, or transmission.
 func (sid *SID) String() (string, error) {
+	// From https://docs.microsoft.com/en-us/windows/win32/secbiomet/general-constants
+	const SecurityMaxSidSize = 68
 	var s *uint16
 	e := ConvertSidToStringSid(sid, &s)
 	if e != nil {
 		return "", e
 	}
 	defer LocalFree((Handle)(unsafe.Pointer(s)))
-	return UTF16ToString((*[256]uint16)(unsafe.Pointer(s))[:]), nil
+	return UTF16ToString((*[SecurityMaxSidSize]uint16)(unsafe.Pointer(s))[:]), nil
 }
 
 // Len returns the length, in bytes, of a valid security identifier sid.

src/syscall/syscall_bsd.go

@@ -242,7 +242,7 @@ func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {
 				break
 			}
 		}
-		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
+		bytes := (*[len(pp.Path)]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
 		sa.Name = string(bytes)
 		return sa, nil
 

src/syscall/syscall_linux.go

@@ -484,7 +484,7 @@ func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {
 		for n < len(pp.Path) && pp.Path[n] != 0 {
 			n++
 		}
-		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
+		bytes := (*[len(pp.Path)]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
 		sa.Name = string(bytes)
 		return sa, nil
 

src/syscall/syscall_solaris.go

@@ -293,7 +293,7 @@ func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {
 		for n < len(pp.Path) && pp.Path[n] != 0 {
 			n++
 		}
-		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
+		bytes := (*[len(pp.Path)]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
 		sa.Name = string(bytes)
 		return sa, nil
 

src/syscall/syscall_windows.go

@@ -765,7 +765,7 @@ func (rsa *RawSockaddrAny) Sockaddr() (Sockaddr, error) {
 		for n < len(pp.Path) && pp.Path[n] != 0 {
 			n++
 		}
-		bytes := (*[10000]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
+		bytes := (*[len(pp.Path)]byte)(unsafe.Pointer(&pp.Path[0]))[0:n]
 		sa.Name = string(bytes)
 		return sa, nil