[B.A.T.M.A.N.] [PATCH] batman-adv: recompute mac_len at the beginning of the rx path

[B.A.T.M.A.N.] [PATCH] batman-adv: recompute mac_len at the beginning of the rx path

[Antonio Quartulli]

It is possible that the mac_len is not properly exported because of strange
device configuration (this behaviour has been observed when using batman-adv on
top of a vlan interface). Therefore it is needed to explicitly recompute it at
the very beginning of the rx path

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
---
 main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/main.c b/main.c
index f9bcfa1..4ef39b6 100644
--- a/main.c
+++ b/main.c
@@ -245,6 +245,12 @@ int batadv_batman_skb_recv(struct sk_buff *skb, struct net_device *dev,
 	if (unlikely(!pskb_may_pull(skb, 2)))
 		goto err_free;
 
+	/* sometimes the mac_len value is not properly computed (e.g. when using
+	 * batman-adv on top of a vlan interface), therefore we need to
+	 * explicitly recompute it here
+	 */
+	skb_reset_mac_len(skb);
+
 	/* expect a valid ethernet header here. */
 	if (unlikely(skb->mac_len != ETH_HLEN || !skb_mac_header(skb)))
 		goto err_free;
-- 
1.7.12

Re: [B.A.T.M.A.N.] [PATCH] batman-adv: recompute mac_len at the beginning of the rx path

[Antonio Quartulli]

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On Sat, Sep 15, 2012 at 02:34:21 +0200, Antonio Quartulli wrote:
> It is possible that the mac_len is not properly exported because of strange
> device configuration (this behaviour has been observed when using batman-adv on
> top of a vlan interface). Therefore it is needed to explicitly recompute it at
> the very beginning of the rx path
> 
> Signed-off-by: Antonio Quartulli <ordex@autistici.org>

Instead of merging this patch I think that the best approach would be to fix the
problem in VLAN code in the kernel.
I'll try to send a patch to netdev.

Cheers,


-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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Re: [B.A.T.M.A.N.] [PATCH] batman-adv: recompute mac_len at the beginning of the rx path

[Simon Wunderlich]

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Hey Antonio,

although I agree that it is the better way to get the fix in the kernel instead of
batman-adv, it would be good to have a workaround in batman-adv for out-of-tree
versions.

I've just sent a (pretty dirty) suggestion, another idea would be to get patches in
the various distributions (openwrt, debian, gentoo, ...) - which would still leave
the problem open for the next "source" release.

Cheers,
	Simon

On Sat, Sep 29, 2012 at 01:27:57PM +0200, Antonio Quartulli wrote:
> On Sat, Sep 15, 2012 at 02:34:21 +0200, Antonio Quartulli wrote:
> > It is possible that the mac_len is not properly exported because of strange
> > device configuration (this behaviour has been observed when using batman-adv on
> > top of a vlan interface). Therefore it is needed to explicitly recompute it at
> > the very beginning of the rx path
> > 
> > Signed-off-by: Antonio Quartulli <ordex@autistici.org>
> 
> Instead of merging this patch I think that the best approach would be to fix the
> problem in VLAN code in the kernel.
> I'll try to send a patch to netdev.
> 
> Cheers,
> 
> 
> -- 
> Antonio Quartulli
> 
> ..each of us alone is worth nothing..
> Ernesto "Che" Guevara



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[B.A.T.M.A.N.] [RFC] batman-adv: dirty hack to recompute mac_len in the rx path

[Simon Wunderlich]

It is possible that the mac_len is not properly exported because of
strange device configuration (this behaviour has been observed when
using batman-adv on top of a vlan interface). Therefore it is needed to
explicitly recompute it at the very beginning of the rx path.

This is done by appending the recompute function to the skb_share_mac()
function, hence the "dirty hack" in the subject. We expect this problem to
be fixed in linux 3.8 and above.

Reported-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
---

this is a rewrite of Antonios patch
"batman-adv: recompute mac_len at the beginning of the rx path". It is
intended to fix the issue for out-of-kernel releases, without hurting
the in-kernel code too much. Obviously, this patch won't go upstream
into the kernel.
---
 compat.h |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/compat.h b/compat.h
index 14969e0..dca9685 100644
--- a/compat.h
+++ b/compat.h
@@ -159,4 +159,19 @@ static inline void eth_hw_addr_random(struct net_device *dev)
 
 #endif /* < KERNEL_VERSION(3, 5, 0) */
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 8, 0)
+
+/* hack for not correctly set mac_len. This may happen for some special
+ * configurations like batman-adv on VLANs.
+ *
+ * This is pretty dirty, but we only use skb_share_check() in main.c right
+ * before mac_len is checked, and the recomputation shouldn't hurt too much.
+ */
+#define skb_share_check(skb, b) \
+	skb_share_check(skb, b); \
+	if (skb) \
+		skb_reset_mac_len(skb)
+
+#endif /* < KERNEL_VERSION(3, 8, 0) */
+
 #endif /* _NET_BATMAN_ADV_COMPAT_H_ */
-- 
1.7.10

Re: [B.A.T.M.A.N.] [RFC] batman-adv: dirty hack to recompute mac_len in the rx path

[Marek Lindner]

On Tuesday, October 02, 2012 04:53:28 Simon Wunderlich wrote:
> +#define skb_share_check(skb, b) \
> +       skb_share_check(skb, b); \
> +       if (skb) \
> +               skb_reset_mac_len(skb)
> +
> +#endif /* < KERNEL_VERSION(3, 8, 0) */

Has this patch been tested ? Our skb_share_check() call is this:
skb = skb_share_check(skb, GFP_ATOMIC);

Now we replace this function call with 2 function calls and 2 return values ?


Cheers,
Marek

Re: [B.A.T.M.A.N.] [RFC] batman-adv: dirty hack to recompute mac_len in the rx path

[Simon Wunderlich]

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Hello Marek,

On Tue, Oct 02, 2012 at 01:16:40PM +0800, Marek Lindner wrote:
> On Tuesday, October 02, 2012 04:53:28 Simon Wunderlich wrote:
> > +#define skb_share_check(skb, b) \
> > +       skb_share_check(skb, b); \
> > +       if (skb) \
> > +               skb_reset_mac_len(skb)
> > +
> > +#endif /* < KERNEL_VERSION(3, 8, 0) */
> 
> Has this patch been tested ? Our skb_share_check() call is this:
> skb = skb_share_check(skb, GFP_ATOMIC);
> 
> Now we replace this function call with 2 function calls and 2 return values ?

I have not tested in a real machine, but only the first function will
return the skb. The second part is a separate statement. I've checked
it with gcc -E (preprocessor only), these lines in main.c will expand to:

 hard_iface = ({ const typeof( ((struct batadv_hard_iface *)0)->batman_adv_ptype ) *__mptr = (ptype); (struct batadv_hard_iface *)( (char *)__mptr - __builtin_offsetof(struct batadv_hard_iface,batman_adv_ptype) );})
                       ;
 skb = skb_share_check(skb, ((( gfp_t)0x20u))); if (skb) skb_reset_mac_len(skb);


 if (!skb)
  goto err_out;

As you can see, the skb = skb_share_check() statement stays at it is, and
the reset_mac_len() is done afterwards.

Cheers,
	Simon


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Re: [B.A.T.M.A.N.] [RFC] batman-adv: dirty hack to recompute mac_len in the rx path

[Sven Eckelmann]

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On Monday 01 October 2012 22:53:28 Simon Wunderlich wrote:
> It is possible that the mac_len is not properly exported because of
> strange device configuration (this behaviour has been observed when
> using batman-adv on top of a vlan interface). Therefore it is needed to
> explicitly recompute it at the very beginning of the rx path.
> 
> This is done by appending the recompute function to the skb_share_mac()
> function, hence the "dirty hack" in the subject. We expect this problem to
> be fixed in linux 3.8 and above.
> 
> Reported-by: Antonio Quartulli <ordex@autistici.org>
> Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
> ---
> 
> this is a rewrite of Antonios patch
> "batman-adv: recompute mac_len at the beginning of the rx path". It is
> intended to fix the issue for out-of-kernel releases, without hurting
> the in-kernel code too much. Obviously, this patch won't go upstream
> into the kernel.
> ---
>  compat.h |   15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/compat.h b/compat.h
> index 14969e0..dca9685 100644
> --- a/compat.h
> +++ b/compat.h
> @@ -159,4 +159,19 @@ static inline void eth_hw_addr_random(struct net_device
> *dev)
> 
>  #endif /* < KERNEL_VERSION(3, 5, 0) */
> 
> +#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 8, 0)
> +
> +/* hack for not correctly set mac_len. This may happen for some special
> + * configurations like batman-adv on VLANs.
> + *
> + * This is pretty dirty, but we only use skb_share_check() in main.c right
> + * before mac_len is checked, and the recomputation shouldn't hurt too
> much. + */
> +#define skb_share_check(skb, b) \
> +	skb_share_check(skb, b); \
> +	if (skb) \
> +		skb_reset_mac_len(skb)
> +
> +#endif /* < KERNEL_VERSION(3, 8, 0) */
> +
>  #endif /* _NET_BATMAN_ADV_COMPAT_H_ */

Can we try a more sane solution like

#define skb_share_check(skb, b) \
	({ \
		struct sk_buff *_t_skb; \
		_t_skb = skb_share_check(skb, b); \
		if (_t_skb) \
			skb_reset_mac_len(_t_skb); \
		_t_skb; \
	})

Please test whether this thing really works and compiles. I just wrote it 
doing something else and never compiled it.

Kind regards,
	Sven

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[B.A.T.M.A.N.] [PATCH] batman-adv: dirty hack to recompute mac_len in the rx path

[Simon Wunderlich]

It is possible that the mac_len is not properly exported because of
strange device configuration (this behaviour has been observed when
using batman-adv on top of a vlan interface). Therefore it is needed to
explicitly recompute it at the very beginning of the rx path.

This is done by appending the recompute function to the skb_share_mac()
function, hence the "dirty hack" in the subject. We expect this problem to
be fixed in linux 3.8 and above.

Reported-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
---

this is a rewrite of Antonios patch
"batman-adv: recompute mac_len at the beginning of the rx path". It is
intended to fix the issue for out-of-kernel releases, without hurting
the in-kernel code too much. Obviously, this patch won't go upstream
into the kernel.

This version includes Svens "more sane" version, and also has implements
skb_reset_mac_len() for kernels prior to 3.0.
---
 compat.h |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/compat.h b/compat.h
index 14969e0..47223f5 100644
--- a/compat.h
+++ b/compat.h
@@ -137,6 +137,11 @@ void batadv_free_rcu_neigh_node(struct rcu_head *rcu);
 void batadv_free_rcu_tt_local_entry(struct rcu_head *rcu);
 void batadv_free_rcu_backbone_gw(struct rcu_head *rcu);
 
+static inline void skb_reset_mac_len(struct sk_buff *skb)
+{
+	skb->mac_len = skb->network_header - skb->mac_header;
+}
+
 #endif /* < KERNEL_VERSION(3, 0, 0) */
 
 
@@ -159,4 +164,23 @@ static inline void eth_hw_addr_random(struct net_device *dev)
 
 #endif /* < KERNEL_VERSION(3, 5, 0) */
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 8, 0)
+
+/* hack for not correctly set mac_len. This may happen for some special
+ * configurations like batman-adv on VLANs.
+ *
+ * This is pretty dirty, but we only use skb_share_check() in main.c right
+ * before mac_len is checked, and the recomputation shouldn't hurt too much.
+ */
+#define skb_share_check(skb, b) \
+	({ \
+		struct sk_buff *_t_skb; \
+		_t_skb = skb_share_check(skb, b); \
+		if (_t_skb) \
+			skb_reset_mac_len(_t_skb); \
+		_t_skb; \
+	})
+
+#endif /* < KERNEL_VERSION(3, 8, 0) */
+
 #endif /* _NET_BATMAN_ADV_COMPAT_H_ */
-- 
1.7.10

Re: [B.A.T.M.A.N.] [PATCH] batman-adv: dirty hack to recompute mac_len in the rx path

[Marek Lindner]

On Sunday, October 14, 2012 20:46:57 Simon Wunderlich wrote:
> It is possible that the mac_len is not properly exported because of
> strange device configuration (this behaviour has been observed when
> using batman-adv on top of a vlan interface). Therefore it is needed to
> explicitly recompute it at the very beginning of the rx path.
> 
> This is done by appending the recompute function to the skb_share_mac()
> function, hence the "dirty hack" in the subject. We expect this problem to
> be fixed in linux 3.8 and above.
> 
> Reported-by: Antonio Quartulli <ordex@autistici.org>
> Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
> ---
> 
> this is a rewrite of Antonios patch
> "batman-adv: recompute mac_len at the beginning of the rx path". It is
> intended to fix the issue for out-of-kernel releases, without hurting
> the in-kernel code too much. Obviously, this patch won't go upstream
> into the kernel.
> 
> This version includes Svens "more sane" version, and also has implements
> skb_reset_mac_len() for kernels prior to 3.0.
> ---
>  compat.h |   24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)

Applied in revision a6ad857.

Thanks,
Marek