[PATCH net] dsa: tag_dsa: Fix mask for trunked packets

A packet received on a trunk will have bit 2 set in Forward DSA tagged
frame. Bit 1 can be either 0 or 1 and is otherwise undefined and bit 0
indicates the frame CFI. Masking with 7 thus results in frames as
being identified as being from a trunk when in fact they are not. Fix
the mask to just look at bit 2.

Fixes: 5b60dadb71db ("net: dsa: tag_dsa: Support reception of packets from LAG devices")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
 net/dsa/tag_dsa.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/dsa/tag_dsa.c b/net/dsa/tag_dsa.c
index 77d0ce89ab77..e5127b7d1c6a 100644
--- a/net/dsa/tag_dsa.c
+++ b/net/dsa/tag_dsa.c

@@ -210,7 +210,7 @@ static struct sk_buff *dsa_rcv_ll(struct sk_buff *skb, struct net_device *dev,
 	cmd = dsa_header[0] >> 6;
 	switch (cmd) {
 	case DSA_CMD_FORWARD:
-		trunk = !!(dsa_header[1] & 7);
+		trunk = !!(dsa_header[1] & 4);
 		break;
 
 	case DSA_CMD_TO_CPU:

-- 
2.33.0

On Sun, Oct 03, 2021 at 05:50:53PM +0200, Andrew Lunn wrote:

A packet received on a trunk will have bit 2 set in Forward DSA tagged
frame. Bit 1 can be either 0 or 1 and is otherwise undefined and bit 0
indicates the frame CFI. Masking with 7 thus results in frames as
being identified as being from a trunk when in fact they are not. Fix
the mask to just look at bit 2.

Fixes: 5b60dadb71db ("net: dsa: tag_dsa: Support reception of packets from LAG devices")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

At least this appears correct on 88E6096/97, but I would expect it to be
true for the entire family.

Would like to hear Tobias' feedback too, though.

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Sun,  3 Oct 2021 17:50:53 +0200 you wrote:

A packet received on a trunk will have bit 2 set in Forward DSA tagged
frame. Bit 1 can be either 0 or 1 and is otherwise undefined and bit 0
indicates the frame CFI. Masking with 7 thus results in frames as
being identified as being from a trunk when in fact they are not. Fix
the mask to just look at bit 2.

Fixes: 5b60dadb71db ("net: dsa: tag_dsa: Support reception of packets from LAG devices")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>

[...]

Here is the summary with links:
  - [net] dsa: tag_dsa: Fix mask for trunked packets
    https://git.kernel.org/netdev/net/c/b44d52a50bc6

You are awesome, thank you!
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