From cc43d9a3d77069850f993fbc4ae47c941bf284b9 Mon Sep 17 00:00:00 2001 From: Daniel Axtens Date: Thu, 16 Sep 2021 01:29:54 +1000 Subject: [PATCH 19/32] 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 Reviewed-by: Daniel Kiper --- 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 906ec7d678..135faac035 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")); } -- 2.34.1