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net/dns: Fix double-free addresses on corrupt DNS response

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grub_net_dns_lookup() takes as inputs a pointer to an array of addresses
("addresses") for the given name, and pointer to a number of addresses
("naddresses"). grub_net_dns_lookup() is responsible for allocating
"addresses", and the caller is responsible for freeing it if
"naddresses" > 0.

The DNS recv_hook will sometimes set and free the addresses array,
for example if the packet is too short:

      if (ptr + 10 >= nb->tail)
	{
	  if (!*data->naddresses)
	    grub_free (*data->addresses);
	  grub_netbuff_free (nb);
	  return GRUB_ERR_NONE;
	}

Later on the nslookup command code unconditionally frees the "addresses"
array. Normally this is fine: the array is either populated with valid
data or is NULL. But in these sorts of error cases it is neither NULL
nor valid and we get a double-free.

Only free "addresses" if "naddresses" > 0.

It looks like the other use of grub_net_dns_lookup() is not affected.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Daniel Axtens 2021-09-16 01:29:54 +10:00 committed by Julian Andres Klode
parent 2a4f87df65
commit 21158c5dfb
1 changed files with 4 additions and 2 deletions
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6
grub-core/net/dns.c
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@ -667,9 +667,11 @@ grub_cmd_nslookup (struct grub_command *cmd __attribute__ ((unused)),
grub_net_addr_to_str (&addresses[i], buf);
grub_printf ("%s\n", buf);
}
grub_free (addresses);
if (naddresses)
return GRUB_ERR_NONE;
{
grub_free (addresses);
return GRUB_ERR_NONE;
}
return grub_error (GRUB_ERR_NET_NO_DOMAIN, N_("no DNS record found"));
}