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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Thu, 16 Sep 2021 01:29:54 +1000
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Subject: [PATCH] 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
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("addresses") for the given name, and pointer to a number of addresses
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("naddresses"). grub_net_dns_lookup() is responsible for allocating
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"addresses", and the caller is responsible for freeing it if
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"naddresses" > 0.
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The DNS recv_hook will sometimes set and free the addresses array,
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for example if the packet is too short:
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if (ptr + 10 >= nb->tail)
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{
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if (!*data->naddresses)
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grub_free (*data->addresses);
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grub_netbuff_free (nb);
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return GRUB_ERR_NONE;
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}
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Later on the nslookup command code unconditionally frees the "addresses"
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array. Normally this is fine: the array is either populated with valid
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data or is NULL. But in these sorts of error cases it is neither NULL
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nor valid and we get a double-free.
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Only free "addresses" if "naddresses" > 0.
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It looks like the other use of grub_net_dns_lookup() is not affected.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit eb2e69fcf51307757e43f55ee8c9354d1ee42dd1)
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(cherry picked from commit d801a27e7acec6c1a83067fab0bb975877eaf704)
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(cherry picked from commit 4d8b6e36ddfda4084e370b3b08c432e8a462e9be)
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---
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grub-core/net/dns.c | 6 ++++--
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1 file changed, 4 insertions(+), 2 deletions(-)
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diff --git a/grub-core/net/dns.c b/grub-core/net/dns.c
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index 906ec7d678..135faac035 100644
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--- a/grub-core/net/dns.c
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+++ b/grub-core/net/dns.c
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@@ -667,9 +667,11 @@ grub_cmd_nslookup (struct grub_command *cmd __attribute__ ((unused)),
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grub_net_addr_to_str (&addresses[i], buf);
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grub_printf ("%s\n", buf);
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}
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- grub_free (addresses);
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if (naddresses)
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- return GRUB_ERR_NONE;
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+ {
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+ grub_free (addresses);
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+ return GRUB_ERR_NONE;
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+ }
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return grub_error (GRUB_ERR_NET_NO_DOMAIN, N_("no DNS record found"));
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}
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