Re: [Libguestfs] [PATCH libnbd 2/9] golang: aio_buffer.go: Make it safer to use

If a Go program tries to use AioBuffer after calling AioBuffer.Free(), the program may silently corrupt data, accessing memory that does not belong to the buffer any more, or segfault if the address is not mapped. In the worst case, it can corrupt memory silently. Calling Free() twice may silently free unrelated memory. Make the buffer safer to use by Freeing only on the first call and setting the pointer to nil. This makes multiple calls to Free() harmless, just like the underlying C.free(). Trying to access Bytes() and Get() after calling Free() will always panic now, revealing the bug in the program. Trying to use AioBuffer with libnbd API will likely segfault and panic. I did not try to test this. Signed-off-by: Nir Soffer <nsoffer(a)redhat.com&gt; --- golang/aio_buffer.go | 5 +++- golang/libnbd_620_aio_buffer_test.go | 41 ++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+), 1 deletion(-) diff --git a/golang/aio_buffer.go b/golang/aio_buffer.go index 2bc69a01..2b77d6ee 100644 --- a/golang/aio_buffer.go +++ b/golang/aio_buffer.go @@ -46,20 +46,23 @@ func MakeAioBuffer(size uint) AioBuffer { func FromBytes(buf []byte) AioBuffer { size := len(buf) ret := MakeAioBuffer(uint(size)) for i := 0; i < len(buf); i++ { *ret.Get(uint(i)) = buf[i] } return ret } func (b *AioBuffer) Free() { - C.free(b.P) + if b.P != nil { + C.free(b.P) + b.P = nil + }

+++ b/golang/libnbd_620_aio_buffer_test.go @@ -53,20 +53,61 @@ func TestAioBuffer(t *testing.T) {