[Dnsmasq-discuss] [PATCH dnsmasq 1/1] fix SIGSEGV in dbus.c when no dhcp-range is configured

[Stefan Hanreich]

When sending a 'AddDhcpLease' DBus message to a dnsmasq instance that
does not have a dhcp-range configured, then dnsmasq segfaults. This
happens because dnsmasq tries to allocate a lease, but DHCP is not
initialized. lease_allocate returns a null pointer, which is in turn
used by lease_set_hwaddr in the dbus handler, triggering the segfault.
Avoid this by adding a null check and returning early from the dbus
handler with an error.

This has already been reported previously here [1].

[1] https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2024q4/017851.html

Signed-off-by: Stefan Hanreich <s.hanreich at proxmox.com>
---
 src/dbus.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/dbus.c b/src/dbus.c
index dac92ed..b734f85 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -612,13 +612,21 @@ static DBusMessage *dbus_add_lease(DBusMessage* message)
       if (!(lease = lease6_find_by_addr(&addr.addr6, 128, 0)))
 	lease = lease6_allocate(&addr.addr6,
 				is_temporary ? LEASE_TA : LEASE_NA);
-      lease_set_iaid(lease, ia_id);
+
+      if (lease) {
+          lease_set_iaid(lease, ia_id);
+      }
     }
 #endif
   else
     return dbus_message_new_error_printf(message, DBUS_ERROR_INVALID_ARGS,
 					 "Invalid IP address '%s'", ipaddr);
    
+  if (!lease) {
+	return dbus_message_new_error_printf(message, DBUS_ERROR_INVALID_ARGS,
+				      "unable to allocate lease for IP address '%s'", ipaddr);
+  }
+
   hw_len = parse_hex((char*)hwaddr, dhcp_chaddr, DHCP_CHADDR_MAX, NULL, &hw_type);
   if (hw_len < 0)
     return dbus_message_new_error_printf(message, DBUS_ERROR_INVALID_ARGS,
-- 
2.47.3