[PATCH v2] net: hsr: Use correct offset for HSR TLV values in supervisory HSR frames

[Lukasz Majewski <lukma@denx.de>]

Current HSR implementation uses following supervisory frame (even for
HSRv1 the HSR tag is not is not present):

00000000: 01 15 4e 00 01 2d XX YY ZZ 94 77 10 88 fb 00 01
00000010: 7e 1c 17 06 XX YY ZZ 94 77 10 1e 06 XX YY ZZ 94
00000020: 77 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00000030: 00 00 00 00 00 00 00 00 00 00 00 00

The current code adds extra two bytes (i.e. sizeof(struct hsr_sup_tlv))
when offset for skb_pull() is calculated.
This is wrong, as both 'struct hsrv1_ethhdr_sp' and 'hsrv0_ethhdr_sp'
already have 'struct hsr_sup_tag' defined in them, so there is no need
for adding extra two bytes.

This code was working correctly as with no RedBox support, the check for
HSR_TLV_EOT (0x00) was off by two bytes, which were corresponding to
zeroed padded bytes for minimal packet size.

Fixes: eafaa88b3eb7 ("net: hsr: Add support for redbox supervision frames")

Signed-off-by: Lukasz Majewski <lukma@denx.de>
---
Changes for v2:
- Update commit message to point to correct commit in "Fixes:"

---
 net/hsr/hsr_forward.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 2afe28712a7a..5d68cb181695 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -83,7 +83,7 @@ static bool is_supervision_frame(struct hsr_priv *hsr, struct sk_buff *skb)
 		return false;
 
 	/* Get next tlv */
-	total_length += sizeof(struct hsr_sup_tlv) + hsr_sup_tag->tlv.HSR_TLV_length;
+	total_length += hsr_sup_tag->tlv.HSR_TLV_length;
 	if (!pskb_may_pull(skb, total_length))
 		return false;
 	skb_pull(skb, total_length);
-- 
2.20.1