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Re: [Qemu-devel] [PATCH for-4.0] migration/ram.c: Fix use-after-free in


From: Philippe Mathieu-Daudé
Subject: Re: [Qemu-devel] [PATCH for-4.0] migration/ram.c: Fix use-after-free in multifd_recv_unfill_packet()
Date: Tue, 9 Apr 2019 20:49:48 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 4/9/19 5:18 PM, Peter Maydell wrote:
> Coverity points out (CID 1400442) that in this code:
> 
>     if (packet->pages_alloc > p->pages->allocated) {
>         multifd_pages_clear(p->pages);
>         multifd_pages_init(packet->pages_alloc);
>     }
> 
> we free p->pages in multifd_pages_clear() but continue to
> use it in the following code. We also leak memory, because
> multifd_pages_init() returns the pointer to a new MultiFDPages_t
> struct but we are ignoring its return value.
> 
> Fix both of these bugs by adding the missing assignment of
> the newly created struct to p->pages.
> 
> Signed-off-by: Peter Maydell <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
> I don't know anything about the multifd code, but this seems like
> the obvious fix based on looking at what the clear and init
> functions are doing. I have only run 'make check' on this,
> so review and testing definitely in order. I think we should
> really put this into 4.0, which means ideally I'd like to
> commit it to master today or tomorrow, though...
> ---
>  migration/ram.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index f68beeeeffc..1ca9ba77b6a 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -851,7 +851,7 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams 
> *p, Error **errp)
>       */
>      if (packet->pages_alloc > p->pages->allocated) {
>          multifd_pages_clear(p->pages);
> -        multifd_pages_init(packet->pages_alloc);
> +        p->pages = multifd_pages_init(packet->pages_alloc);
>      }
>  
>      p->pages->used = be32_to_cpu(packet->pages_used);
> 



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