Re: [Qemu-devel] [PATCH 1/4] migration: fix parameter validation on ram load

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/11/2014 10:44, Michael S. Tsirkin wrote:
> During migration, the values read from migration stream during ram load
> are not validated. Especially offset in host_from_stream_offset() and
> also the length of the writes in the callers of said function.
> 
> To fix this, we need to make sure that the [offset, offset + length]
> range fits into one of the allocated memory regions.
> 
> Validating addr < len should be sufficient since data seems to always be
> managed in TARGET_PAGE_SIZE chunks.
> 
> Fixes: CVE-2014-7840
> 
> Note: follow-up patches add extra checks on each block->host access.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  arch_init.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 88a5ba0..593a990 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -1006,7 +1006,7 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>      uint8_t len;
>  
>      if (flags & RAM_SAVE_FLAG_CONTINUE) {
> -        if (!block) {
> +        if (!block || block->length <= offset) {
>              error_report("Ack, bad migration stream!");
>              return NULL;
>          }
> @@ -1019,8 +1019,9 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>      id[len] = 0;
>  
>      QTAILQ_FOREACH(block, &ram_list.blocks, next) {
> -        if (!strncmp(id, block->idstr, sizeof(id)))
> +        if (!strncmp(id, block->idstr, sizeof(id)) && block->length > offset) {
>              return memory_region_get_ram_ptr(block->mr) + offset;
> +        }
>      }
>  
>      error_report("Can't find block %s!", id);
> 

Sort-of Yoda conditionals, i.e. I think "offset >= block->length" and
"offset < block->length" would have been more common and indeed that's
what you use in patch 3.  That's the only comment I have.

Series

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>