netdev - [PATCH] tcp_nv: fix potential integer overflow in tcpnv

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Message-ID: <20180131042147.GA13245@embeddedgus>
Date:   Tue, 30 Jan 2018 22:21:48 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: [PATCH] tcp_nv: fix potential integer overflow in tcpnv_acked

Add suffix ULL to constant 80000 in order to avoid a potential integer
overflow and give the compiler complete information about the proper
arithmetic to use. Notice that this constant is used in a context that
expects an expression of type u64.

The current cast to u64 effectively applies to the whole expression
as an argument of type u64 to be passed to div64_u64, but it does
not prevent it from being evaluated using 32-bit arithmetic instead
of 64-bit arithmetic.

Also, once the expression is properly evaluated using 64-bit arithmentic,
there is no need for the parentheses and the external cast to u64.

Addresses-Coverity-ID: 1357588 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 net/ipv4/tcp_nv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
index ddbce73..764298e 100644
--- a/net/ipv4/tcp_nv.c
+++ b/net/ipv4/tcp_nv.c
@@ -364,7 +364,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
 		 */
 		cwnd_by_slope = (u32)
 			div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt,
-				  (u64)(80000 * tp->mss_cache));
+				  80000ULL * tp->mss_cache);
 		max_win = cwnd_by_slope + nv_pad;

 		/* If cwnd > max_win, decrease cwnd
-- 
2.7.4