netdev - Re: [PATCH] bonding: Always assign be16 value to vlan

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Date:   Thu, 20 Apr 2023 12:47:33 -0700
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     Simon Horman <horms@...nel.org>
cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: Always assign be16 value to vlan_proto

Simon Horman <horms@...nel.org> wrote:

>The type of the vlan_proto field is __be16.
>And most users of the field use it as such.
>
>In the case of setting or testing the field for the
>special VLAN_N_VID value, host byte order is used.
>Which seems incorrect.
>
>Address this issue by converting VLAN_N_VID to __be16.
>
>I don't believe this is a bug because VLAN_N_VID in
>both little-endian (and big-endian) byte order does
>not conflict with any valid values (0 through VLAN_N_VID - 1)
>in big-endian byte order.

	Is that true for all cases, or am I just confused?  Doesn't VLAN
ID 16 match VLAN_N_VID (which is 4096) if byte swapped?

	I.e., on a little endian host, VLAN_N_VID is 0x1000 natively,
and network byte order (big endian) of VLAN ID 16 is also 0x1000.

	Either way, I think the change is fine; VLAN_N_VID is being used
as a sentinel value here, so the only real requirement is that it not
match an actual VLAN ID in network byte order.

	-J

>Reported by sparse as:
>
> .../bond_main.c:2857:26: warning: restricted __be16 degrades to integer
> .../bond_main.c:2863:20: warning: restricted __be16 degrades to integer
> .../bond_main.c:2939:40: warning: incorrect type in assignment (different base types)
> .../bond_main.c:2939:40:    expected restricted __be16 [usertype] vlan_proto
> .../bond_main.c:2939:40:    got int
>
>No functional changes intended.
>Compile tested only.
>
>Signed-off-by: Simon Horman <horms@...nel.org>
>---
> drivers/net/bonding/bond_main.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index db7e650d9ebb..7f4c75fe58e1 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -2854,13 +2854,13 @@ static bool bond_handle_vlan(struct slave *slave, struct bond_vlan_tag *tags,
> 	struct net_device *slave_dev = slave->dev;
> 	struct bond_vlan_tag *outer_tag = tags;
> 
>-	if (!tags || tags->vlan_proto == VLAN_N_VID)
>+	if (!tags || tags->vlan_proto == cpu_to_be16(VLAN_N_VID))
> 		return true;
> 
> 	tags++;
> 
> 	/* Go through all the tags backwards and add them to the packet */
>-	while (tags->vlan_proto != VLAN_N_VID) {
>+	while (tags->vlan_proto != cpu_to_be16(VLAN_N_VID)) {
> 		if (!tags->vlan_id) {
> 			tags++;
> 			continue;
>@@ -2936,7 +2936,7 @@ struct bond_vlan_tag *bond_verify_device_path(struct net_device *start_dev,
> 		tags = kcalloc(level + 1, sizeof(*tags), GFP_ATOMIC);
> 		if (!tags)
> 			return ERR_PTR(-ENOMEM);
>-		tags[level].vlan_proto = VLAN_N_VID;
>+		tags[level].vlan_proto = cpu_to_be16(VLAN_N_VID);
> 		return tags;
> 	}

---
	-Jay Vosburgh, jay.vosburgh@...onical.com