[PATCH net 2/2] net: dccp: switch rx_tstamp_last_feedback to monotonic clock

[Eric Dumazet]

To compute delays, better not use time of the day which can
be changed by admins or malicious programs.

Also change ccid3_first_li() to use s64 type for delta variable
to avoid potential overflows.

Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Gerrit Renker <ger...@erg.abdn.ac.uk>
Cc: d...@vger.kernel.org
---
 net/dccp/ccids/ccid3.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 
d57a2be1e2e09aee89347e286aca538303b7dee1..12877a1514e7b8e873cd26529e58f7ebaae99c1a
 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -600,7 +600,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk,
 {
        struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
        struct dccp_sock *dp = dccp_sk(sk);
-       ktime_t now = ktime_get_real();
+       ktime_t now = ktime_get();
        s64 delta = 0;
 
        switch (fbtype) {
@@ -632,7 +632,7 @@ static void ccid3_hc_rx_send_feedback(struct sock *sk,
                return;
        }
 
-       ccid3_pr_debug("Interval %ldusec, X_recv=%u, 1/p=%u\n", (long)delta,
+       ccid3_pr_debug("Interval %lldusec, X_recv=%u, 1/p=%u\n", delta,
                       hc->rx_x_recv, hc->rx_pinv);
 
        hc->rx_tstamp_last_feedback = now;
@@ -679,7 +679,8 @@ static int ccid3_hc_rx_insert_options(struct sock *sk, 
struct sk_buff *skb)
 static u32 ccid3_first_li(struct sock *sk)
 {
        struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
-       u32 x_recv, p, delta;
+       u32 x_recv, p;
+       s64 delta;
        u64 fval;
 
        if (hc->rx_rtt == 0) {
@@ -687,7 +688,9 @@ static u32 ccid3_first_li(struct sock *sk)
                hc->rx_rtt = DCCP_FALLBACK_RTT;
        }
 
-       delta  = ktime_to_us(net_timedelta(hc->rx_tstamp_last_feedback));
+       delta = ktime_us_delta(ktime_get(), hc->rx_tstamp_last_feedback);
+       if (delta <= 0)
+               delta = 1;
        x_recv = scaled_div32(hc->rx_bytes_recv, delta);
        if (x_recv == 0) {              /* would also trigger divide-by-zero */
                DCCP_WARN("X_recv==0\n");
-- 
2.18.0.rc2.346.g013aa6912e-goog