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From 21158c5dfb5e0c5015277346128903397d498da4 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Thu, 16 Sep 2021 01:29:54 +1000
Subject: net/dns: Fix double-free addresses on corrupt DNS response
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>
---
grub-core/net/dns.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/grub-core/net/dns.c b/grub-core/net/dns.c
index 906ec7d67..135faac03 100644
--- a/grub-core/net/dns.c
+++ b/grub-core/net/dns.c
@@ -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"));
}
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