[PATCH] netpoll: Fix device name check in netpoll_setup()

[PATCH] netpoll: Fix device name check in netpoll_setup()

[Matthias Kaehlcke]

Apparently netpoll_setup() assumes that netpoll.dev_name is a pointer
when checking if the device name is set:

if (np->dev_name) {
  ...

However the field is a character array, therefore the condition always
yields true. Check instead whether the first byte of the array has a
non-zero value.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 net/core/netpoll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 8357f164c660..912731bed7b7 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -666,7 +666,7 @@ int netpoll_setup(struct netpoll *np)
 	int err;
 
 	rtnl_lock();
-	if (np->dev_name) {
+	if (np->dev_name[0]) {
 		struct net *net = current->nsproxy->net_ns;
 		ndev = __dev_get_by_name(net, np->dev_name);
 	}
-- 
2.14.0.rc0.284.gd933b75aa4-goog

Re: [PATCH] netpoll: Fix device name check in netpoll_setup()

[Doug Anderson]

Hi,

On Tue, Jul 25, 2017 at 11:36 AM, Matthias Kaehlcke <mka@chromium.org> wrote:
> Apparently netpoll_setup() assumes that netpoll.dev_name is a pointer
> when checking if the device name is set:
>
> if (np->dev_name) {
>   ...
>
> However the field is a character array, therefore the condition always
> yields true. Check instead whether the first byte of the array has a
> non-zero value.
>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  net/core/netpoll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
> index 8357f164c660..912731bed7b7 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -666,7 +666,7 @@ int netpoll_setup(struct netpoll *np)
>         int err;
>
>         rtnl_lock();
> -       if (np->dev_name) {
> +       if (np->dev_name[0]) {
>                 struct net *net = current->nsproxy->net_ns;
>                 ndev = __dev_get_by_name(net, np->dev_name);
>         }

It's really up to the maintainer of the code, but my first instinct
here would be to instead remove the "if" test unless we really expect
dev->dev_name to be blank in lots of cases.  It will slightly slow
down the error case but should avoid an "if" test in the non-error
case.  By definition it should be safe since currently the "if" test
should always evaluate to true.

-Doug

Re: [PATCH] netpoll: Fix device name check in netpoll_setup()

[Cong Wang]

On Wed, Jul 26, 2017 at 11:44 AM, Doug Anderson <dianders@chromium.org> wrote:
> Hi,
>
> On Tue, Jul 25, 2017 at 11:36 AM, Matthias Kaehlcke <mka@chromium.org> wrote:
>> Apparently netpoll_setup() assumes that netpoll.dev_name is a pointer
>> when checking if the device name is set:
>>
>> if (np->dev_name) {
>>   ...
>>
>> However the field is a character array, therefore the condition always
>> yields true. Check instead whether the first byte of the array has a
>> non-zero value.
>>
>> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>>  net/core/netpoll.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/core/netpoll.c b/net/core/netpoll.c
>> index 8357f164c660..912731bed7b7 100644
>> --- a/net/core/netpoll.c
>> +++ b/net/core/netpoll.c
>> @@ -666,7 +666,7 @@ int netpoll_setup(struct netpoll *np)
>>         int err;
>>
>>         rtnl_lock();
>> -       if (np->dev_name) {
>> +       if (np->dev_name[0]) {
>>                 struct net *net = current->nsproxy->net_ns;
>>                 ndev = __dev_get_by_name(net, np->dev_name);
>>         }
>
> It's really up to the maintainer of the code, but my first instinct
> here would be to instead remove the "if" test unless we really expect
> dev->dev_name to be blank in lots of cases.  It will slightly slow
> down the error case but should avoid an "if" test in the non-error
> case.  By definition it should be safe since currently the "if" test
> should always evaluate to true.
>

netconsole could set this dev_name to empty via configfs,
so this patch is correct.

Re: [PATCH] netpoll: Fix device name check in netpoll_setup()

[David Miller]

From: Matthias Kaehlcke <mka@chromium.org>
Date: Tue, 25 Jul 2017 11:36:25 -0700

> Apparently netpoll_setup() assumes that netpoll.dev_name is a pointer
> when checking if the device name is set:
> 
> if (np->dev_name) {
>   ...
> 
> However the field is a character array, therefore the condition always
> yields true. Check instead whether the first byte of the array has a
> non-zero value.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

Applied, thanks a lot.