Re: [Qemu-devel] [PATCH v2] curl: Don't deref NULL pointer in call to aio_poll.

["Benoît Canet" <benoit.canet@irqsave.net>]

The Thursday 28 Aug 2014 à 09:04:21 (+0100), Richard W.M. Jones wrote :
> In commit 63f0f45f2e89b60ff8245fec81328ddfde42a303 the following
> mechanical change was made:
> 
>          if (!state) {
> -            qemu_aio_wait();
> +            aio_poll(state->s->aio_context, true);
>          }
> 
> The new code now checks if state is NULL and then dereferences it
> ('state->s') which is obviously incorrect.
> 
> This commit replaces state->s->aio_context with
> bdrv_get_aio_context(bs), fixing this problem.  The two other hunks
> are concerned with getting the BlockDriverState pointer bs to where it
> is needed.
> 
> The original bug causes a segfault when using libguestfs to access a
> VMware vCenter Server and doing any kind of complex read-heavy
> operations.  With this commit the segfault goes away.
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/curl.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/curl.c b/block/curl.c
> index d4b85d2..f59615d 100644
> --- a/block/curl.c
> +++ b/block/curl.c
> @@ -352,7 +352,7 @@ static void curl_multi_timeout_do(void *arg)
>  #endif
>  }
>  
> -static CURLState *curl_init_state(BDRVCURLState *s)
> +static CURLState *curl_init_state(BlockDriverState *bs, BDRVCURLState *s)
>  {
>      CURLState *state = NULL;
>      int i, j;
> @@ -370,7 +370,7 @@ static CURLState *curl_init_state(BDRVCURLState *s)
>              break;
>          }
>          if (!state) {
> -            aio_poll(state->s->aio_context, true);
> +            aio_poll(bdrv_get_aio_context(bs), true);
>          }
>      } while(!state);
>  
> @@ -541,7 +541,7 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
>      DPRINTF("CURL: Opening %s\n", file);
>      s->aio_context = bdrv_get_aio_context(bs);
>      s->url = g_strdup(file);
> -    state = curl_init_state(s);
> +    state = curl_init_state(bs, s);
>      if (!state)
>          goto out_noclean;
>  
> @@ -625,7 +625,7 @@ static void curl_readv_bh_cb(void *p)
>      }
>  
>      // No cache found, so let's start a new request
> -    state = curl_init_state(s);
> +    state = curl_init_state(acb->common.bs, s);
>      if (!state) {
>          acb->common.cb(acb->common.opaque, -EIO);
>          qemu_aio_release(acb);
> -- 
> 2.0.4
> 
> 
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>