Due to the use of a uint8_t to index inside the DNS payload we could end
up in an infinite loop when specific (invalid) DNS packets were
processed by ovn-controller. In the infinite loop we keep increasing the
query_name dynamic string until running out of memory.
One way to replicate the issue is to configure DNS on the logical switch
and then inject a manually crafted DNS-like packet. For example, with
Scapy:
>>> p = IP(dst='10.0.0.2',src='10.0.0.3')/UDP(dport=53)/('a'*364)
>>> send(p)
Also add a sanity check on minimum L4 size of packets.
CC: Numan Siddique <[email protected]>
Fixes: 16cb4fb8ca49 ("ovn-controller: Add 'dns_lookup' action")
Reported-at: https://bugzilla.redhat.com/1740335
Reported-by: Priscila <[email protected]>
Signed-off-by: Dumitru Ceara <[email protected]>
---
controller/pinctrl.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/controller/pinctrl.c b/controller/pinctrl.c
index f27718f..365a0d1 100644
--- a/controller/pinctrl.c
+++ b/controller/pinctrl.c
@@ -1628,6 +1628,12 @@ pinctrl_handle_dns_lookup(
goto exit;
}
+ /* Check that the packet stores at least the minimal headers. */
+ if (dp_packet_l4_size(pkt_in) < (UDP_HEADER_LEN + DNS_HEADER_LEN)) {
+ VLOG_WARN_RL(&rl, "truncated dns packet");
+ goto exit;
+ }
+
/* Extract the DNS header */
struct dns_header const *in_dns_header = dp_packet_get_udp_payload(pkt_in);
if (!in_dns_header) {
@@ -1652,7 +1658,7 @@ pinctrl_handle_dns_lookup(
uint8_t *end = (uint8_t *)in_udp + MIN(udp_len, l4_len);
uint8_t *in_dns_data = (uint8_t *)(in_dns_header + 1);
uint8_t *in_queryname = in_dns_data;
- uint8_t idx = 0;
+ uint16_t idx = 0;
struct ds query_name;
ds_init(&query_name);
/* Extract the query_name. If the query name is - 'www.ovn.org' it would be
--
1.8.3.1
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