Re: [PATCH v3] exec: set map length to zero when returning NULL

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/26/20 9:50 AM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> When mapping physical memory into host's virtual address space,
> 'address_space_map' may return NULL if BounceBuffer is in_use.
> Set and return '*plen = 0' to avoid later NULL pointer dereference.
> 
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  exec.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> Update v3: set *plen = 0;
>   -> https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg06249.html
> 
> diff --git a/exec.c b/exec.c
> index 5162f0d12f..4eea84bf66 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3538,6 +3538,7 @@ void *address_space_map(AddressSpace *as,
>  
>      if (!memory_access_is_direct(mr, is_write)) {
>          if (atomic_xchg(&bounce.in_use, true)) {
> +            *plen = 0;
>              return NULL;
>          }
>          /* Avoid unbounded allocations */
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>