unix: avoid converting non-pointers to unsafe.Pointer in PtraceIO

Despite having the misleading type "void*" in the C API, the "offs"
field of the ptrace_io_desc struct is an offset within the child
process, and thus is not necessarily a valid pointer at all in the
parent process. The Go unsafe.Pointer type must refer only to valid
pointers, so converting this field through unsafe.Pointer is incorrect
and (in some cases) dangerous.

While we're here, let's also rename the "addr" function argument to
"offs", since that's the corresponding ptrace_io_desc field. It's very
confusing to have a function argument named "attr" that doesn't map to
the struct field of the same name!

For golang/go#58351.

Change-Id: Id899f823e8d398b51fb0c42f466d7ae2f957c26b
Reviewed-on: https://go-review.googlesource.com/c/sys/+/465675
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>

unix/syscall_freebsd_386.go

@@ -60,8 +60,13 @@ func PtraceGetFsBase(pid int, fsbase *int64) (err error) {
 	return ptrace(PT_GETFSBASE, pid, uintptr(unsafe.Pointer(fsbase)), 0)
 }
 
-func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
-	ioDesc := PtraceIoDesc{Op: int32(req), Offs: uintptr(unsafe.Pointer(addr)), Addr: uintptr(unsafe.Pointer(&out[0])), Len: uint32(countin)}
+func PtraceIO(req int, pid int, offs uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{
+		Op:   int32(req),
+		Offs: offs,
+		Addr: uintptr(unsafe.Pointer(&out[0])), // TODO(#58351): this is not safe.
+		Len:  uint32(countin),
+	}
 	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
 	return int(ioDesc.Len), err
 }

unix/syscall_freebsd_amd64.go

@@ -60,8 +60,13 @@ func PtraceGetFsBase(pid int, fsbase *int64) (err error) {
 	return ptrace(PT_GETFSBASE, pid, uintptr(unsafe.Pointer(fsbase)), 0)
 }
 
-func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
-	ioDesc := PtraceIoDesc{Op: int32(req), Offs: uintptr(unsafe.Pointer(addr)), Addr: uintptr(unsafe.Pointer(&out[0])), Len: uint64(countin)}
+func PtraceIO(req int, pid int, offs uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{
+		Op:   int32(req),
+		Offs: offs,
+		Addr: uintptr(unsafe.Pointer(&out[0])), // TODO(#58351): this is not safe.
+		Len:  uint64(countin),
+	}
 	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
 	return int(ioDesc.Len), err
 }

unix/syscall_freebsd_arm.go

@@ -56,8 +56,13 @@ func sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 
 func Syscall9(num, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
-func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
-	ioDesc := PtraceIoDesc{Op: int32(req), Offs: uintptr(unsafe.Pointer(addr)), Addr: uintptr(unsafe.Pointer(&out[0])), Len: uint32(countin)}
+func PtraceIO(req int, pid int, offs uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{
+		Op:   int32(req),
+		Offs: offs,
+		Addr: uintptr(unsafe.Pointer(&out[0])), // TODO(#58351): this is not safe.
+		Len:  uint32(countin),
+	}
 	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
 	return int(ioDesc.Len), err
 }

unix/syscall_freebsd_arm64.go

@@ -56,8 +56,13 @@ func sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 
 func Syscall9(num, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
-func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
-	ioDesc := PtraceIoDesc{Op: int32(req), Offs: uintptr(unsafe.Pointer(addr)), Addr: uintptr(unsafe.Pointer(&out[0])), Len: uint64(countin)}
+func PtraceIO(req int, pid int, offs uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{
+		Op:   int32(req),
+		Offs: offs,
+		Addr: uintptr(unsafe.Pointer(&out[0])), // TODO(#58351): this is not safe.
+		Len:  uint64(countin),
+	}
 	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
 	return int(ioDesc.Len), err
 }

unix/syscall_freebsd_riscv64.go

@@ -56,8 +56,13 @@ func sendfile(outfd int, infd int, offset *int64, count int) (written int, err e
 
 func Syscall9(num, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err syscall.Errno)
 
-func PtraceIO(req int, pid int, addr uintptr, out []byte, countin int) (count int, err error) {
-	ioDesc := PtraceIoDesc{Op: int32(req), Offs: uintptr(unsafe.Pointer(addr)), Addr: uintptr(unsafe.Pointer(&out[0])), Len: uint64(countin)}
+func PtraceIO(req int, pid int, offs uintptr, out []byte, countin int) (count int, err error) {
+	ioDesc := PtraceIoDesc{
+		Op:   int32(req),
+		Offs: offs,
+		Addr: uintptr(unsafe.Pointer(&out[0])), // TODO(#58351): this is not safe.
+		Len:  uint64(countin),
+	}
 	err = ptrace(PT_IO, pid, uintptr(unsafe.Pointer(&ioDesc)), 0)
 	return int(ioDesc.Len), err
 }