Re: [Qemu-devel] [PATCH] util/async: avoid NULL pointer dereference

[Fam Zheng <famz@redhat.com>]

On Mon, 06/11 15:04, Jie Wang wrote:
> if laio_init create linux_aio failed and return NULL, NULL pointer
> dereference will occur when laio_attach_aio_context dereference
> linux_aio in aio_get_linux_aio, so add assert to avoid it.
> 
> Signed-off-by: Jie Wang <wangjie88@huawei.com>
> ---
>  util/async.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/util/async.c b/util/async.c
> index 03f62787f2..7766bcd8bc 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -327,6 +327,7 @@ LinuxAioState *aio_get_linux_aio(AioContext *ctx)
>  {
>      if (!ctx->linux_aio) {
>          ctx->linux_aio = laio_init();
> +        assert(ctx->linux_aio);
>          laio_attach_aio_context(ctx->linux_aio, ctx);
>      }
>      return ctx->linux_aio;
> -- 

I'm afraid this is not the correct fix. If laio_init() can fail, this function
should skip laio_attach_aio_context() and return NULL, then callers should check
the return value and handle the error. E.g. Set s->use_linux_aio to false and
fall back to posix I/O, and perhaps report the error with error_report. Or even
better, call laio_init during raw_open and use error_setg(errp, ...).

assert() will simply crash the program, it is not the right way to catch errors.

Fam