[PATCH] net: ncsi: Adding padding bytes in the payload

Update NC-SI command handler (both standard and OEM) to take into
account of payload paddings in allocating skb (in case of payload
size is not 32-bit aligned).

The checksum field follows payload field, without taking payload
padding into account can cause checksum being truncated, leading to
dropped packets.

Signed-off-by: Kumar Thangavel <redacted>

---
 net/ncsi/ncsi-cmd.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/net/ncsi/ncsi-cmd.c b/net/ncsi/ncsi-cmd.c
index ba9ae482141b..4625fc935603 100644
--- a/net/ncsi/ncsi-cmd.c
+++ b/net/ncsi/ncsi-cmd.c

@@ -214,11 +214,19 @@ static int ncsi_cmd_handler_oem(struct sk_buff *skb,
 	struct ncsi_cmd_oem_pkt *cmd;
 	unsigned int len;
 
+	/* NC-SI spec requires payload to be padded with 0
+	 * to 32-bit boundary before the checksum field.
+	 * Ensure the padding bytes are accounted for in
+	 * skb allocation
+	 */
+
+	unsigned short payload = ALIGN(nca->payload, 4);
+
 	len = sizeof(struct ncsi_cmd_pkt_hdr) + 4;
-	if (nca->payload < 26)
+	if (payload < 26)
 		len += 26;
 	else
-		len += nca->payload;
+		len += payload;
 
 	cmd = skb_put_zero(skb, len);
 	memcpy(&cmd->mfr_id, nca->data, nca->payload);

@@ -272,6 +280,7 @@ static struct ncsi_request *ncsi_alloc_command(struct ncsi_cmd_arg *nca)
 	struct net_device *dev = nd->dev;
 	int hlen = LL_RESERVED_SPACE(dev);
 	int tlen = dev->needed_tailroom;
+	int payload;
 	int len = hlen + tlen;
 	struct sk_buff *skb;
 	struct ncsi_request *nr;

@@ -281,14 +290,18 @@ static struct ncsi_request *ncsi_alloc_command(struct ncsi_cmd_arg *nca)
 		return NULL;
 
 	/* NCSI command packet has 16-bytes header, payload, 4 bytes checksum.
+	 * Payload needs padding so that the checksum field follwoing payload is
+	 * aligned to 32bit boundary.
 	 * The packet needs padding if its payload is less than 26 bytes to
 	 * meet 64 bytes minimal ethernet frame length.
 	 */
 	len += sizeof(struct ncsi_cmd_pkt_hdr) + 4;
-	if (nca->payload < 26)
+
+	payload = ALIGN(nca->payload, 4);
+	if (payload < 26)
 		len += 26;
 	else
-		len += nca->payload;
+		len += payload;
 
 	/* Allocate skb */
 	skb = alloc_skb(len, GFP_ATOMIC);

-- 
2.17.1

Dear Kumar,


Thank you for your patch.

Nit: Could you please use the imperative mood in the commit message summary:

 > net: ncsi: Add padding bytes in the payload

Or more descriptive:

 > net: ncsi: Padd payload to be 32-bit aligned to fix dropped packets

Am 12.10.21 um 08:22 schrieb Kumar Thangavel:

Update NC-SI command handler (both standard and OEM) to take into
account of payload paddings in allocating skb (in case of payload
size is not 32-bit aligned).

The checksum field follows payload field, without taking payload
padding into account can cause checksum being truncated, leading to
dropped packets.

How can this be reproduced?

It’d be great, if you included the specification version, and section if 
the requirement.

+	 * to 32-bit boundary before the checksum field.
+	 * Ensure the padding bytes are accounted for in
+	 * skb allocation
+	 */
+

Please remove the blank line.

following

+	 * aligned to 32bit boundary.

32-bit

  	 * The packet needs padding if its payload is less than 26 bytes to
  	 * meet 64 bytes minimal ethernet frame length.
  	 */
  	len += sizeof(struct ncsi_cmd_pkt_hdr) + 4;
-	if (nca->payload < 26)
+
+	payload = ALIGN(nca->payload, 4);
+	if (payload < 26)
  		len += 26;
  	else
-		len += nca->payload;
+		len += payload;
  
  	/* Allocate skb */
  	skb = alloc_skb(len, GFP_ATOMIC);

Besides the nits, this looks fine to me.


Kind regards,

Paul

On Tue, 12 Oct 2021 at 06:23, Kumar Thangavel
[off-list ref] wrote:

Update NC-SI command handler (both standard and OEM) to take into
account of payload paddings in allocating skb (in case of payload
size is not 32-bit aligned).

The checksum field follows payload field, without taking payload
padding into account can cause checksum being truncated, leading to
dropped packets.

Can you help us review this by pointing out where this is described in
the NCSI spec?

We've been running this code for a number of years now and I wonder
why this hasn't been a problem so far.

Cheers,

Joel

On Tue, 2021-10-12 at 22:44 +0000, Joel Stanley wrote:

On Tue, 12 Oct 2021 at 06:23, Kumar Thangavel
[off-list ref] wrote:

quoted

Update NC-SI command handler (both standard and OEM) to take into
account of payload paddings in allocating skb (in case of payload
size is not 32-bit aligned).

The checksum field follows payload field, without taking payload
padding into account can cause checksum being truncated, leading to
dropped packets.

Can you help us review this by pointing out where this is described in
the NCSI spec?

We've been running this code for a number of years now and I wonder
why this hasn't been a problem so far.

I'm assuming this is referencing section 8.2.2.2:
If the payload is present and does not end on a 32-bit boundary, one to
three padding bytes equal to 0x00 shall be present to align the
checksum field to a 32-bit boundary.

But I'm also surprised this hasn't caused issues so far if we've been
getting it wrong. Is there an example that reproduces the issue?

Cheers,
Sam

Cheers,

Joel

quoted

Signed-off-by: Kumar Thangavel <redacted>

---
 net/ncsi/ncsi-cmd.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/net/ncsi/ncsi-cmd.c b/net/ncsi/ncsi-cmd.c
index ba9ae482141b..4625fc935603 100644
--- a/net/ncsi/ncsi-cmd.c
+++ b/net/ncsi/ncsi-cmd.c

@@ -214,11 +214,19 @@ static int ncsi_cmd_handler_oem(struct sk_buff

*skb,
        struct ncsi_cmd_oem_pkt *cmd;
        unsigned int len;

+       /* NC-SI spec requires payload to be padded with 0
+        * to 32-bit boundary before the checksum field.
+        * Ensure the padding bytes are accounted for in
+        * skb allocation
+        */
+
+       unsigned short payload = ALIGN(nca->payload, 4);
+
        len = sizeof(struct ncsi_cmd_pkt_hdr) + 4;
-       if (nca->payload < 26)
+       if (payload < 26)
                len += 26;
        else
-               len += nca->payload;
+               len += payload;

        cmd = skb_put_zero(skb, len);
        memcpy(&cmd->mfr_id, nca->data, nca->payload);

@@ -272,6 +280,7 @@ static struct ncsi_request

*ncsi_alloc_command(struct ncsi_cmd_arg *nca)
        struct net_device *dev = nd->dev;
        int hlen = LL_RESERVED_SPACE(dev);
        int tlen = dev->needed_tailroom;
+       int payload;
        int len = hlen + tlen;
        struct sk_buff *skb;
        struct ncsi_request *nr;

@@ -281,14 +290,18 @@ static struct ncsi_request

*ncsi_alloc_command(struct ncsi_cmd_arg *nca)
                return NULL;

        /* NCSI command packet has 16-bytes header, payload, 4 bytes
checksum.
+        * Payload needs padding so that the checksum field follwoing
payload is
+        * aligned to 32bit boundary.
         * The packet needs padding if its payload is less than 26
bytes to
         * meet 64 bytes minimal ethernet frame length.
         */
        len += sizeof(struct ncsi_cmd_pkt_hdr) + 4;
-       if (nca->payload < 26)
+
+       payload = ALIGN(nca->payload, 4);
+       if (payload < 26)
                len += 26;
        else
-               len += nca->payload;
+               len += payload;

        /* Allocate skb */
        skb = alloc_skb(len, GFP_ATOMIC);
--
2.17.1