[PATCH net-next 2/3] tcp: avoid integer overflows in tcp_rcv_space_adjust()

[Eric Dumazet]

When using large tcp_rmem[2] values (I did tests with 500 MB),
I noticed overflows while computing rcvwin.

Lets fix this before the following patch.

Signed-off-by: Eric Dumazet <eduma...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Wei Wang <wei...@google.com>
---
 include/linux/tcp.h  |  2 +-
 net/ipv4/tcp_input.c | 12 +++++++-----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 
ca4a6361389b8a3b268ca5b0f4778662a1f7d315..4f93f0953c411322dc6403af7d1b9b6c3e30bd4f
 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -344,7 +344,7 @@ struct tcp_sock {
 
 /* Receiver queue space */
        struct {
-               int     space;
+               u32     space;
                u32     seq;
                u64     time;
        } rcvq_space;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 
746a6773c482f5d419ddc9d7c9d52949cbb74cfb..2900e58738cde0ad1ab4a034b6300876ac276edb
 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -576,8 +576,8 @@ static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 void tcp_rcv_space_adjust(struct sock *sk)
 {
        struct tcp_sock *tp = tcp_sk(sk);
+       u32 copied;
        int time;
-       int copied;
 
        tcp_mstamp_refresh(tp);
        time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
@@ -600,12 +600,13 @@ void tcp_rcv_space_adjust(struct sock *sk)
 
        if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
-               int rcvwin, rcvmem, rcvbuf;
+               int rcvmem, rcvbuf;
+               u64 rcvwin;
 
                /* minimal window to cope with packet losses, assuming
                 * steady state. Add some cushion because of small variations.
                 */
-               rcvwin = (copied << 1) + 16 * tp->advmss;
+               rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
 
                /* If rate increased by 25%,
                 *      assume slow start, rcvwin = 3 * copied
@@ -625,8 +626,9 @@ void tcp_rcv_space_adjust(struct sock *sk)
                while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
                        rcvmem += 128;
 
-               rcvbuf = min(rcvwin / tp->advmss * rcvmem,
-                            sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
+               do_div(rcvwin, tp->advmss);
+               rcvbuf = min_t(u64, rcvwin * rcvmem,
+                              sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
                if (rcvbuf > sk->sk_rcvbuf) {
                        sk->sk_rcvbuf = rcvbuf;
 
-- 
2.15.1.424.g9478a66081-goog