[PATCH AUTOSEL 4.14 03/32] batman-adv: Fix segfault when writing to throughput_override

From: Sasha Levin
Date: Mon Oct 08 2018 - 11:26:38 EST

From: Sven Eckelmann <sven@xxxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxx>
Acked-by: Marek Lindner <mareklindner@xxxxxxxxxxxxx>
Signed-off-by: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
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 0ae8b30e4eaa..ec412c5b8697 100644
--- a/net/batman-adv/sysfs.c
+++ b/net/batman-adv/sysfs.c
@@ -1078,8 +1078,9 @@ 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);