linux-kernel - [PATCH 4.4 029/114] net/mlx4_en: Resolve dividing by zero in 32-bit system

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Message-Id: <20181108215101.728604370@linuxfoundation.org>
Date:   Thu,  8 Nov 2018 13:50:44 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eugenia Emantayev <eugenia@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 029/114] net/mlx4_en: Resolve dividing by zero in 32-bit system

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 4850cf4581578216468b7b3c3d06cc5abb0a697d ]

When doing roundup_pow_of_two for large enough number with
bit 31, an overflow will occur and a value equal to 1 will
be returned. In this case 1 will be subtracted from the return
value and division by zero will be reached.

Fixes: 31c128b66e5b ("net/mlx4_en: Choose time-stamping shift value according to HW frequency")
Signed-off-by: Eugenia Emantayev <eugenia@...lanox.com>
Signed-off-by: Tariq Toukan <tariqt@...lanox.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/ethernet/mellanox/mlx4/en_clock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_clock.c b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
index 4dccf7287f0f..52e4ed2f639d 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_clock.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_clock.c
@@ -251,8 +251,11 @@ static u32 freq_to_shift(u16 freq)
 {
 	u32 freq_khz = freq * 1000;
 	u64 max_val_cycles = freq_khz * 1000 * MLX4_EN_WRAP_AROUND_SEC;
+	u64 tmp_rounded =
+		roundup_pow_of_two(max_val_cycles) > max_val_cycles ?
+		roundup_pow_of_two(max_val_cycles) - 1 : UINT_MAX;
 	u64 max_val_cycles_rounded = is_power_of_2(max_val_cycles + 1) ?
-		max_val_cycles : roundup_pow_of_two(max_val_cycles) - 1;
+		max_val_cycles : tmp_rounded;
 	/* calculate max possible multiplier in order to fit in 64bit */
 	u64 max_mul = div_u64(0xffffffffffffffffULL, max_val_cycles_rounded);
 
-- 
2.17.1