24.01.2017 03:36, Matthew Garrett пишет:
> The current logic in the DNS resolution code allocates an address buffer
> based on the number of addresses in the response packet. If we receive
> multiple response packets in response to a single query packet, this means
> that we will reallocate a new buffer large enough for only the addresses in
> that specific packet, discarding any previous results in the process. Worse,
> we still keep track of the *total* number of addresses resolved in response
> to this query, not merely the number in the packet being currently processed.
> Use realloc() rather than malloc() to avoid overwriting the existing data,
> and allocate a buffer large enough for the total set of addresses rather
> than merely the number in this specific response.
> ---
> grub-core/net/dns.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/grub-core/net/dns.c b/grub-core/net/dns.c
> index 5d9afe0..5deb1ef 100644
> --- a/grub-core/net/dns.c
> +++ b/grub-core/net/dns.c
> @@ -285,8 +285,8 @@ recv_hook (grub_net_udp_socket_t sock __attribute__
> ((unused)),
> ptr++;
> ptr += 4;
> }
> - *data->addresses = grub_malloc (sizeof ((*data->addresses)[0])
> - * grub_be_to_cpu16 (head->ancount));
> + *data->addresses = grub_realloc (*data->addresses, sizeof
> ((*data->addresses)[0])
> + * (grub_be_to_cpu16 (head->ancount) + *data->naddresses));
If *data->addresses was not NULL, we should not reach this code.
/* Code apparently assumed that only one packet is received as response.
We may get multiple responses due to network condition, so check here
and quit early. */
if (*data->addresses)
{
grub_netbuff_free (nb);
return GRUB_ERR_NONE;
}
This was noted previously by Josef, we discussed it and my position is
that resolver code requires redesign to correctly merge multiple answers
and prioritize A vs AAAA requests.
Do you get actual errors with current master? If yes, could you provide
more information what this patch fixes?
> if (!*data->addresses)
> {
> grub_errno = GRUB_ERR_NONE;
>
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