Re: [PATCH v1] migration: fix RAMBlock add NULL check

[Peter Xu <peterx@redhat.com>]

On Tue, Oct 10, 2023 at 01:48:53PM +0300, Dmitry Frolov wrote:
> qemu_ram_block_from_host() may return NULL, which will be dereferenced w/o

AFAIU this path is only called from trusted sites, so I don't see why it
can be NULL?  Do you have any scenario that can trigger this?

> check. Usualy return value is checked for this function.
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: c7c0e72408df5e7821c0e995122fb2fe0ac001f1 ("migration/ram: Handle RAM block resizes during precopy")

Normally if we attach Fixes it means we want to backport it to stable.
Here I'd like to double check on above to see whether we'd need a Fixes.

> Signed-off-by: Dmitry Frolov <frolov@swemel.ru>

The patch itself looks all fine; though if I'm going to add some print, I'd
print something more to make it at least try to be more useful (host,
old_size, new_size).  I had a feeling that we can already assert.

Thanks,

> ---
>  migration/ram.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index e4bfd39f08..bd4b7574e1 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -4281,6 +4281,11 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
>      RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset);
>      Error *err = NULL;
>  
> +    if (!rb) {
> +        error_report("RAM block not found");
> +        return;
> +    }
> +
>      if (migrate_ram_is_ignored(rb)) {
>          return;
>      }
> -- 
> 2.34.1
> 
> 

-- 
Peter Xu