linux-kernel - [PATCH] iio: adf4350: fix a possible divided-by-zero bug in adf4350_set

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Date:   Fri, 21 May 2021 14:19:53 +0800
From:   tq17373059@...a.edu.cn
To:     lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju@...nghua.edu.cn, Qi Teng <tq17373059@...a.edu.cn>,
        TOTE Robot <oslab@...nghua.edu.cn>
Subject: [PATCH] iio: adf4350: fix a possible divided-by-zero bug in adf4350_set_freq()

From: Qi Teng <tq17373059@...a.edu.cn>

The variable st->r1_mod is checked in:
  if (st->r0_fract && st->r1_mod)

This indicates that st->r1_mod can be zero. Its value is the same as
that in:
  st->r0_fract = do_div(tmp, st->r1_mod);

However, st->r1_mod performs as a divisor in this statement, which
implies a possible divided-by-zero bug.

To fix this possible bug, st->r1_mod is checked before the division
operation. If it is zero, st->r0_fract is set to zero instead of
do_div(tmp, st->r1_mod).

Reported-by: TOTE Robot <oslab@...nghua.edu.cn> 
Signed-off-by: Qi Teng <tq17373059@...a.edu.cn>
---
 drivers/iio/frequency/adf4350.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/iio/frequency/adf4350.c b/drivers/iio/frequency/adf4350.c
index 99c6f260cc21..1462a6a5bc6d 100644
--- a/drivers/iio/frequency/adf4350.c
+++ b/drivers/iio/frequency/adf4350.c
@@ -182,10 +182,7 @@ static int adf4350_set_freq(struct adf4350_state *st, unsigned long long freq)
 
 		tmp = freq * (u64)st->r1_mod + (st->fpfd >> 1);
 		do_div(tmp, st->fpfd); /* Div round closest (n + d/2)/d */
-		if (st->r1_mod)
-			st->r0_fract = do_div(tmp, st->r1_mod);
-		else
-			st->r0_fract = 0;
+		st->r0_fract = do_div(tmp, st->r1_mod);
 		st->r0_int = tmp;
 	} while (mdiv > st->r0_int);
 
-- 
2.25.1