From: Eric Dumazet <edumazet@google.com>

Date: Wed, 26 Jan 2022 17:10:22 -0800

Subject: ipv4: avoid using shared IP generator for connected sockets

Patch-mainline: v5.17-rc2

Git-commit: 23f57406b82de51809d5812afd96f210f8b627f3

References: CVE-2020-36516 bsc#1196616

ip_select_ident_segs() has been very conservative about using

the connected socket private generator only for packets with IP_DF

set, claiming it was needed for some VJ compression implementations.

As mentioned in this referenced document, this can be abused.

(Ref: Off-Path TCP Exploits of the Mixed IPID Assignment)

Before switching to pure random IPID generation and possibly hurt

some workloads, lets use the private inet socket generator.

Not only this will remove one vulnerability, this will also

improve performance of TCP flows using pmtudisc==IP_PMTUDISC_DONT

Fixes: 73f156a6e8c1 ("inetpeer: get rid of ip_id_count")

Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: David Ahern <dsahern@kernel.org>

Reported-by: Ray Che <xijiache@gmail.com>

Cc: Willy Tarreau <w@1wt.eu>

Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Acked-by: Michal Kubecek <mkubecek@suse.cz>

---

 include/net/ip.h | 21 ++++++++++-----------

 1 file changed, 10 insertions(+), 11 deletions(-)

--- a/include/net/ip.h

+++ b/include/net/ip.h

@@ -385,19 +385,18 @@ static inline void ip_select_ident_segs(struct net *net, struct sk_buff *skb,

 {

 	struct iphdr *iph = ip_hdr(skb);

+	/* We had many attacks based on IPID, use the private

+	 * generator as much as we can.

+	 */

+	if (sk && inet_sk(sk)->inet_daddr) {

+		iph->id = htons(inet_sk(sk)->inet_id);

+		inet_sk(sk)->inet_id += segs;

+		return;

+	}

 	if ((iph->frag_off & htons(IP_DF)) && !skb->ignore_df) {

-		/* This is only to work around buggy Windows95/2000

-		 * VJ compression implementations.  If the ID field

-		 * does not change, they drop every other packet in

-		 * a TCP stream using header compression.

-		 */

-		if (sk && inet_sk(sk)->inet_daddr) {

-			iph->id = htons(inet_sk(sk)->inet_id);

-			inet_sk(sk)->inet_id += segs;

-		} else {

-			iph->id = 0;

-		}

+		iph->id = 0;

 	} else {

+		/* Unfortunately we need the big hammer to get a suitable IPID */

 		__ip_select_ident(net, iph, segs);

 	}

 }