Kumar.
On Tue, 2021-10-12 at 22:44 +0000, Joel Stanley wrote:
> On Tue, 12 Oct 2021 at 06:23, Kumar Thangavel
> <kumarthangavel.hcl@gmail.com> 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.
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.
Kumar : Yes. In the NC-SI spec, section 8.2.2.2 represents a 32-bit boundary.
If it does not end on a 32-bit boundary, padding bytes can be added.
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?
Kumar : We have a use case of NIC firmware update in our system which is pldm based and the transport layer is NC-SI based on RBT.
Sending some pldm based commands to NIC. In that, some of the commands failed because of a payload size less than 32.
So, Added padding bytes to align the 32-bit boundary and issues got resolved.
Cheers,
Sam
>
> Cheers,
>
> Joel
>
> >
> > Signed-off-by: Kumar Thangavel <thangavel.k@hcl.com>
> >
> > ---
> > 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
> >