[PATCH 1/1] net/ipv4: discard icmp timestamp requests

[jch@thehaxbys.co.uk]

An icmp timestamp request is classed a a minor security vulnerability
(CVE-1999-0524) due to an information leak.  As pretty much everything
uses NTP these days, it's not as though this is an actual problem but
scanners flag this so for everyone's sake, let's just discard timestamp
requests.

Signed-off-by: John Haxby <jch@thehaxbys.co.uk>
---
 net/ipv4/icmp.c | 42 +-----------------------------------------
 1 file changed, 1 insertion(+), 41 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 23e921d313b3..ec0443424110 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -1383,46 +1383,6 @@ bool icmp_build_probe(struct sk_buff *skb, struct icmphdr *icmphdr)
 	return true;
 }
 
-/*
- *	Handle ICMP Timestamp requests.
- *	RFC 1122: 3.2.2.8 MAY implement ICMP timestamp requests.
- *		  SHOULD be in the kernel for minimum random latency.
- *		  MUST be accurate to a few minutes.
- *		  MUST be updated at least at 15Hz.
- */
-static enum skb_drop_reason icmp_timestamp(struct sk_buff *skb)
-{
-	DEFINE_RAW_FLEX(struct icmp_bxm, icmp_param, replyopts.opt.__data,
-			IP_OPTIONS_DATA_FIXED_SIZE);
-	/*
-	 *	Too short.
-	 */
-	if (skb->len < 4)
-		goto out_err;
-
-	/*
-	 *	Fill in the current time as ms since midnight UT:
-	 */
-	icmp_param->data.times[1] = inet_current_timestamp();
-	icmp_param->data.times[2] = icmp_param->data.times[1];
-
-	BUG_ON(skb_copy_bits(skb, 0, &icmp_param->data.times[0], 4));
-
-	icmp_param->data.icmph	   = *icmp_hdr(skb);
-	icmp_param->data.icmph.type = ICMP_TIMESTAMPREPLY;
-	icmp_param->data.icmph.code = 0;
-	icmp_param->skb		   = skb;
-	icmp_param->offset	   = 0;
-	icmp_param->data_len	   = 0;
-	icmp_param->head_len	   = sizeof(struct icmphdr) + 12;
-	icmp_reply(icmp_param, skb);
-	return SKB_NOT_DROPPED_YET;
-
-out_err:
-	__ICMP_INC_STATS(skb_dst_dev_net_rcu(skb), ICMP_MIB_INERRORS);
-	return SKB_DROP_REASON_PKT_TOO_SMALL;
-}
-
 static enum skb_drop_reason icmp_discard(struct sk_buff *skb)
 {
 	/* pretend it was a success */
@@ -1685,7 +1645,7 @@ static const struct icmp_control icmp_pointers[NR_ICMP_TYPES + 1] = {
 		.error = 1,
 	},
 	[ICMP_TIMESTAMP] = {
-		.handler = icmp_timestamp,
+		.handler = icmp_discard,
 	},
 	[ICMP_TIMESTAMPREPLY] = {
 		.handler = icmp_discard,
-- 
2.55.0