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[PATCH 3/4] Don't allocate a new address buffer if we receive multiple D

From: Matthew Garrett
Subject: [PATCH 3/4] Don't allocate a new address buffer if we receive multiple DNS responses
Date: Mon, 23 Jan 2017 16:36:00 -0800

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__ 
       ptr += 4;
-  *data->addresses = grub_malloc (sizeof ((*data->addresses)[0])
-                                * grub_be_to_cpu16 (head->ancount));
+  *data->addresses = grub_realloc (*data->addresses, sizeof 
+                    * (grub_be_to_cpu16 (head->ancount) + *data->naddresses));
   if (!*data->addresses)
       grub_errno = GRUB_ERR_NONE;

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