From:   Ameer Hamza <amhamza.mgc@gmail.com>
To:     davem@davemloft.net, kuba@kernel.org, mcoquelin.stm32@gmail.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     amhamza.mgc@gmail.com, h.assmann@pengutronix.de
Subject: [PATCH v2] net: stmmac: Fix possible division by zero
Date:   Mon,  6 Dec 2021 19:23:37 +0500
Message-Id: <20211206142337.28602-1-amhamza.mgc@gmail.com>
In-Reply-To: <20211203173708.7fdbed06@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
References: <20211203173708.7fdbed06@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In stmmac_init_tstamp_counter() routine, there is a possiblity of division
by zero. If priv->plat->clk_ptp_rate becomes greater than 1 GHz,
config_sub_second_increment() subroutine may calculate sec_inc as zero
depending upon the PTP_TCR_TSCFUPDT register value, which will cause
divide by zero exception.

Fixes: a6da2bbb0005e ("net: stmmac: retain PTP clock time during SIOCSHWTSTAMP ioctls")
Addresses-Coverity: 1494557 ("Division or modulo by zero")
Signed-off-by: Ameer Hamza <amhamza.mgc@gmail.com>

---
Changes in v2:
Added fix tag, bug justification, and commit author.
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index da8306f60730..f44400323407 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -863,7 +863,7 @@ int stmmac_init_tstamp_counter(struct stmmac_priv *priv, u32 systime_flags)
 	stmmac_config_sub_second_increment(priv, priv->ptpaddr,
 					   priv->plat->clk_ptp_rate,
 					   xmac, &sec_inc);
-	temp = div_u64(1000000000ULL, sec_inc);
+	temp = div_u64(1000000000ULL, (sec_inc > 0) ? sec_inc : 1);
 
 	/* Store sub second increment for later use */
 	priv->sub_second_inc = sec_inc;
-- 
2.25.1