Re: [PATCH] net: Adding parameter detection in __ethtool_get_link_ksettings.

On Mon, 2019-08-26 at 17:47 +0800, Dongxu Liu wrote:

quoted

On 8/26/19 9:23 AM, Dongxu Liu wrote:
The __ethtool_get_link_ksettings symbol will be exported,
and external users may use an illegal address.
We should check the parameters before using them,
otherwise the system will crash.

[ 8980.991134] BUG: unable to handle kernel NULL pointer
dereference at           (null)
[ 8980.993049] IP: [<ffffffff8155aca7>]
__ethtool_get_link_ksettings+0x27/0x140
[ 8980.994285] PGD 0
[ 8980.995013] Oops: 0000 [#1] SMP
[ 8980.995896] Modules linked in: sch_ingress ...
[ 8981.013220] CPU: 3 PID: 25174 Comm: kworker/3:3 Tainted:
G           O   ----V-------   3.10.0-327.36.58.4.x86_64 #1
[ 8981.017667] Workqueue: events linkwatch_event
[ 8981.018652] task: ffff8800a8348000 ti: ffff8800b045c000 task.ti:
ffff8800b045c000
[ 8981.020418] RIP: 0010:[<ffffffff8155aca7>]  [<ffffffff8155aca7>]
__ethtool_get_link_ksettings+0x27/0x140
[ 8981.022383] RSP: 0018:ffff8800b045fc88  EFLAGS: 00010202
[ 8981.023453] RAX: 0000000000000000 RBX: ffff8800b045fcac RCX:
0000000000000000
[ 8981.024726] RDX: ffff8800b658f600 RSI: ffff8800b045fcac RDI:
ffff8802296e0000
[ 8981.026000] RBP: ffff8800b045fc98 R08: 0000000000000000 R09:
0000000000000001
[ 8981.027273] R10: 00000000000073e0 R11: 0000082b0cc8adea R12:
ffff8802296e0000
[ 8981.028561] R13: ffff8800b566e8c0 R14: ffff8800b658f600 R15:
ffff8800b566e000
[ 8981.029841] FS:  0000000000000000(0000)
GS:ffff88023ed80000(0000) knlGS:0000000000000000
[ 8981.031715] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 8981.032845] CR2: 0000000000000000 CR3: 00000000b39a9000 CR4:
00000000003407e0
[ 8981.034137] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 8981.035427] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 8981.036702] Stack:
[ 8981.037406]  ffff8800b658f600 0000000000009c40 ffff8800b045fce8
ffffffffa047a71d
[ 8981.039238]  000000000000004d ffff8800b045fcc8 ffff8800b045fd28
ffffffff815cb198
[ 8981.041070]  ffff8800b045fcd8 ffffffff810807e6 00000000e8212951
0000000000000001
[ 8981.042910] Call Trace:
[ 8981.043660]  [<ffffffffa047a71d>]
bond_update_speed_duplex+0x3d/0x90 [bonding]
[ 8981.045424]  [<ffffffff815cb198>] ? inetdev_event+0x38/0x530
[ 8981.046554]  [<ffffffff810807e6>] ? put_online_cpus+0x56/0x80
[ 8981.047688]  [<ffffffffa0480d67>] bond_netdev_event+0x137/0x360
[bonding]
...

Signed-off-by: Dongxu Liu <redacted>
---
 net/core/ethtool.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c index 

6288e69..9a50b64 100644

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c

@@ -545,6 +545,8 @@ int __ethtool_get_link_ksettings(struct

net_device 
*dev,  {
 	ASSERT_RTNL();
 
+	if (!dev || !dev->ethtool_ops)
+		return -EOPNOTSUPP;
I do not believe dev can possibly be NULL at this point.
 	if (!dev->ethtool_ops->get_link_ksettings)
 		return -EOPNOTSUPP;
 

I tried to find an appropriate Fixes: tag.
It seems this particular bug was added either by
Fixes: 9856909c2abb ("net: bonding: use __ethtool_get_ksettings")
or generically in :
Fixes: 3f1ac7a700d0 ("net: ethtool: add new ETHTOOL_xLINKSETTINGS
API")

In fact, "dev->ethtool_ops" is a null pointer in my environment.
I didn't get the case where "dev" is a null pointer.

dev can't be a null pointer since bond driver guarantees that
and there is a check for the case where it could be null in 
bond_slave_netdev_event.

You can drop the "!dev" check, since also it should be the caller
responsibility and we should avoid cluttering the net core code with
such redundant checks.

Maybe "if (!dev->ethtool_ops)" is more accurate for this bug.

Also i am not sure about this, could be a bug in the device driver your
enslaving.

alloc_netdev_mqs will assign &default_ethtool_ops to dev->ethtool_ops ,
if user provided setup callback didn't assign the driver specific
ethtool_ops.

so the device driver must be doing something wrong, overwriting defult
ethtool_ops with a NULL pointer maybe ? and why ?

I found this bug in version 3.10, the function name was
__ethtool_get_settings.
After 3f1ac7a700d0 ("net: ethtool: add new ETHTOOL_xLINKSETTINGS
API"),
This function evolved into __ethtool_get_link_ksettings.