tcp: avoid integer overflows in tcp_rcv_space_adjust()

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 <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Wei Wang <weiwan@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 6 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index ca4a6361389b..4f93f0953c41 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 746a6773c482..2900e58738cd 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;