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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" X-SA-Exim-Connect-IP: 2607:7c80:54:e::133 X-SA-Exim-Mail-From: barebox-bounces+lore=pengutronix.de@lists.infradead.org X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on metis.ext.pengutronix.de X-Spam-Level: X-Spam-Status: No, score=-5.2 required=4.0 tests=AWL,BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.2 Subject: Re: [PATCH] net: dns: Generate and verify transaction ID X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on metis.ext.pengutronix.de) Hi, I would like some feedback on how to select a dns_req_id. Although ths is likely not very critical to barebox, I think using both dns_timer_start plus random32 is a bit overkill. Maybe simply using random is sufficient. On Thu, May 05, 2022 at 12:08:05PM +0200, Jules Maselbas wrote: > The transaction ID wasn't verified on received DNS responses, plus the > ID needs to be difficult to predict in order to avoid MitM (man in the > middle) being able to easily forge responses. > > Signed-off-by: Jules Maselbas > --- > net/dns.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/net/dns.c b/net/dns.c > index 78588b96f..9ad316e33 100644 > --- a/net/dns.c > +++ b/net/dns.c > @@ -58,6 +58,7 @@ struct header { > > static struct net_connection *dns_con; > static uint64_t dns_timer_start; > +static uin32_t dns_req_id; > static int dns_state; > static IPaddr_t dns_ip; > > @@ -70,9 +71,12 @@ static int dns_send(const char *name) > unsigned char *p, *s, *fullname, *dotptr; > const unsigned char *domain; > > + /* generate a random transaction id */ > + dns_req_id = dns_timer_start + random32(); I am wondering if using only one of dns_timer_start or randome32 is sufficient on its own. For the record musl uses clock_gettime without random at all. > /* Prepare DNS packet header */ > header = (struct header *)packet; > - header->tid = 1; > + header->tid = htons(dns_req_id); > header->flags = htons(0x100); /* standard query */ > header->nqueries = htons(1); /* Just one query */ > header->nanswers = 0; > @@ -127,6 +131,10 @@ static void dns_recv(struct header *header, unsigned len) > > pr_debug("%s\n", __func__); > > + /* Only accept responses with the expected request id */ > + if (ntohs(header->id) != dns_req_id) > + return; > + > /* We sent 1 query. We want to see more that 1 answer. */ > if (ntohs(header->nqueries) != 1) > return; > -- > 2.17.1 > _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox