linux-kernel - [PATCH AUTOSEL 4.18 07/58] batman-adv: Fix segfault when writing to throughput

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Message-Id: <20181008152523.70705-7-sashal@kernel.org>
Date:   Mon,  8 Oct 2018 11:24:32 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Sven Eckelmann <sven@...fation.org>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 07/58] batman-adv: Fix segfault when writing to throughput_override

From: Sven Eckelmann <sven@...fation.org>

[ Upstream commit b9fd14c20871e6189f635e49b32d7789e430b3c8 ]

The per hardif sysfs file "batman_adv/throughput_override" prints the
resulting change as info text when the users writes to this file. It uses
the helper function batadv_info to add it at the same time to the kernel
ring buffer and to the batman-adv debug log (when CONFIG_BATMAN_ADV_DEBUG
is enabled).

The function batadv_info requires as first parameter the batman-adv softif
net_device. This parameter is then used to find the private buffer which
contains the debug log for this batman-adv interface. But
batadv_store_throughput_override used as first argument the slave
net_device. This slave device doesn't have the batadv_priv private data
which is access by batadv_info.

Writing to this file with CONFIG_BATMAN_ADV_DEBUG enabled can either lead
to a segfault or to memory corruption.

Fixes: 0b5ecc6811bd ("batman-adv: add throughput override attribute to hard_ifaces")
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Acked-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 net/batman-adv/sysfs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/sysfs.c b/net/batman-adv/sysfs.c
index f2eef43bd2ec..3a76e8970c02 100644
--- a/net/batman-adv/sysfs.c
+++ b/net/batman-adv/sysfs.c
@@ -1090,8 +1090,9 @@ static ssize_t batadv_store_throughput_override(struct kobject *kobj,
 	if (old_tp_override == tp_override)
 		goto out;

-	batadv_info(net_dev, "%s: Changing from: %u.%u MBit to: %u.%u MBit\n",
-		    "throughput_override",
+	batadv_info(hard_iface->soft_iface,
+		    "%s: %s: Changing from: %u.%u MBit to: %u.%u MBit\n",
+		    "throughput_override", net_dev->name,
 		    old_tp_override / 10, old_tp_override % 10,
 		    tp_override / 10, tp_override % 10);

-- 
2.17.1