[PATCH net-next v4 1/2] net: hsr: require valid EOT supervision TLV

[luka.gejak@linux.dev]

From: Luka Gejak <luka.gejak@linux.dev>

Supervision frames are only valid if terminated with a zero-length EOT
TLV. The current check fails to reject non-EOT entries as the terminal
TLV, potentially allowing malformed supervision traffic.

Fix this by strictly requiring the terminal TLV to be HSR_TLV_EOT
with a length of zero.

Reviewed-by: Felix Maurer <fmaurer@redhat.com>
Signed-off-by: Luka Gejak <luka.gejak@linux.dev>
---
 net/hsr/hsr_forward.c | 41 ++++++++++++++++++++++-------------------
 1 file changed, 22 insertions(+), 19 deletions(-)

diff --git a/net/hsr/hsr_forward.c b/net/hsr/hsr_forward.c
index 0aca859c88cb..17b705235c4a 100644
--- a/net/hsr/hsr_forward.c
+++ b/net/hsr/hsr_forward.c
@@ -82,39 +82,42 @@ static bool is_supervision_frame(struct hsr_priv *hsr, struct sk_buff *skb)
 	    hsr_sup_tag->tlv.HSR_TLV_length != sizeof(struct hsr_sup_payload))
 		return false;
 
-	/* Get next tlv */
+	/* Advance past the first TLV payload to reach next TLV header */
 	total_length += hsr_sup_tag->tlv.HSR_TLV_length;
-	if (!pskb_may_pull(skb, total_length))
+	/* Linearize next TLV header before access */
+	if (!pskb_may_pull(skb, total_length + sizeof(struct hsr_sup_tlv)))
 		return false;
 	skb_pull(skb, total_length);
 	hsr_sup_tlv = (struct hsr_sup_tlv *)skb->data;
 	skb_push(skb, total_length);
 
-	/* if this is a redbox supervision frame we need to verify
-	 * that more data is available
+	/* Walk through TLVs to find end-of-TLV marker, skipping any unknown
+	 * extension TLVs to maintain forward compatibility.
 	 */
-	if (hsr_sup_tlv->HSR_TLV_type == PRP_TLV_REDBOX_MAC) {
-		/* tlv length must be a length of a mac address */
-		if (hsr_sup_tlv->HSR_TLV_length != sizeof(struct hsr_sup_payload))
-			return false;
+	for (;;) {
+		if (hsr_sup_tlv->HSR_TLV_type == HSR_TLV_EOT &&
+		    hsr_sup_tlv->HSR_TLV_length == 0)
+			return true;
 
-		/* make sure another tlv follows */
-		total_length += sizeof(struct hsr_sup_tlv) + hsr_sup_tlv->HSR_TLV_length;
-		if (!pskb_may_pull(skb, total_length))
+		/* Validate known TLV types */
+		if (hsr_sup_tlv->HSR_TLV_type == PRP_TLV_REDBOX_MAC) {
+			if (hsr_sup_tlv->HSR_TLV_length !=
+			    sizeof(struct hsr_sup_payload))
+				return false;
+		}
+
+		/* Advance past current TLV: header + payload */
+		total_length += sizeof(struct hsr_sup_tlv) +
+				hsr_sup_tlv->HSR_TLV_length;
+		/* Linearize next TLV header before access */
+		if (!pskb_may_pull(skb,
+				   total_length + sizeof(struct hsr_sup_tlv)))
 			return false;
 
-		/* get next tlv */
 		skb_pull(skb, total_length);
 		hsr_sup_tlv = (struct hsr_sup_tlv *)skb->data;
 		skb_push(skb, total_length);
 	}
-
-	/* end of tlvs must follow at the end */
-	if (hsr_sup_tlv->HSR_TLV_type == HSR_TLV_EOT &&
-	    hsr_sup_tlv->HSR_TLV_length != 0)
-		return false;
-
-	return true;
 }
 
 static bool is_proxy_supervision_frame(struct hsr_priv *hsr,
-- 
2.53.0