[ovs-dev] datapath: Fix an error handling path in 'ovs_nla_init_match_and_action()'

All other error handling paths in this function go through the 'error'
label. This one should do the same.

Fixes: 9cc9a5cb176c ("datapath: Avoid using stack larger than 1024.")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
I think that the comment above the function could be improved. It looks
like the commit log which has introduced this function.

I'm also not sure that commit 9cc9a5cb176c is of any help. It is
supposed to remove a warning, and I guess it does. But 'ovs_nla_init_match_and_action()'
is called unconditionnaly from 'ovs_flow_cmd_set()'. So even if the stack
used by each function is reduced, the overall stack should be the same, if
not larger.

So this commit sounds like adding a bug where the code was fine and states
to fix an issue but, at the best, only hides it.

Instead of fixing the code with the proposed patch, reverting the initial
commit could also be considered.
---
 net/openvswitch/datapath.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Please use a proper Subject subsystem prefix for openvswitch patches.
"datapath" isn't very specific in the global kernel namespace at all.

The entire networking stack packet processing path is a "datapath"

"openvswitch: " would have been much better.

On 09/11/2017 12:20 PM, Christophe JAILLET wrote:
> All other error handling paths in this function go through the 'error'
> label. This one should do the same.
> 
> Fixes: 9cc9a5cb176c ("datapath: Avoid using stack larger than 1024.")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> I think that the comment above the function could be improved. It looks
> like the commit log which has introduced this function.
> 
> I'm also not sure that commit 9cc9a5cb176c is of any help. It is
> supposed to remove a warning, and I guess it does. But 'ovs_nla_init_match_and_action()'
> is called unconditionnaly from 'ovs_flow_cmd_set()'. So even if the stack
> used by each function is reduced, the overall stack should be the same, if
> not larger.
> 
> So this commit sounds like adding a bug where the code was fine and states
> to fix an issue but, at the best, only hides it.

Having a large stack frame isn't really a bug per se.  But the Linux kernel
warns about stack frames that are too large so reordering the code to
get the warning to go away seems fine to me.

> 
> Instead of fixing the code with the proposed patch, reverting the initial
> commit could also be considered.

Then the warning will come back.

- Greg

> ---
>   net/openvswitch/datapath.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index 76cf273a56c7..c3aec6227c91 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -1112,7 +1112,8 @@ static int ovs_nla_init_match_and_action(struct net *net,
>   		if (!a[OVS_FLOW_ATTR_KEY]) {
>   			OVS_NLERR(log,
>   				  "Flow key attribute not present in set flow.");
> -			return -EINVAL;
> +			error = -EINVAL;
> +			goto error;
>   		}
>   
>   		*acts = get_flow_actions(net, a[OVS_FLOW_ATTR_ACTIONS], key,
>

On Tue, Sep 12, 2017 at 3:20 AM, Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
> All other error handling paths in this function go through the 'error'
> label. This one should do the same.
>
> Fixes: 9cc9a5cb176c ("datapath: Avoid using stack larger than 1024.")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> I think that the comment above the function could be improved. It looks
> like the commit log which has introduced this function.
>
> I'm also not sure that commit 9cc9a5cb176c is of any help. It is
> supposed to remove a warning, and I guess it does. But 'ovs_nla_init_match_and_action()'
> is called unconditionnaly from 'ovs_flow_cmd_set()'. So even if the stack
> used by each function is reduced, the overall stack should be the same, if
> not larger.
>
> So this commit sounds like adding a bug where the code was fine and states
> to fix an issue but, at the best, only hides it.
>
> Instead of fixing the code with the proposed patch, reverting the initial
> commit could also be considered.
> ---
>  net/openvswitch/datapath.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index 76cf273a56c7..c3aec6227c91 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -1112,7 +1112,8 @@ static int ovs_nla_init_match_and_action(struct net *net,
>                 if (!a[OVS_FLOW_ATTR_KEY]) {
>                         OVS_NLERR(log,
>                                   "Flow key attribute not present in set flow.");
> -                       return -EINVAL;
> +                       error = -EINVAL;
> +                       goto error;

Thank for your report. But I really don't understand.
In the 'ovs_nla_init_match_and_action', we only init 'match' when the
OVS_FLOW_ATTR_KEY is set.
If the 'OVS_FLOW_ATTR_ACTIONS' is set, but not 'OVS_FLOW_ATTR_KEY', we
can return directly because the match is not inited yet, and it is
unnecessary to set it's mask NULL. Then ovs_flow_cmd_set can run via
value returned.


>                 }
>
>                 *acts = get_flow_actions(net, a[OVS_FLOW_ATTR_ACTIONS], key,
> --
> 2.11.0
>