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SubjectRE: [PATCH net-next] net/ncsi: support unaligned payload size in NC-SI cmd handler
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That is right. It is necessary to adjust the len for padding on both places.

Thanks,
Justin


> > > 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: Ben Wei <benwei@fb.com>
> >
> > If you have to align and add padding, I do not see where you are
> > clearing out that padding memory to make sure it is initialized.
> >
> > You do comparisons with 'payload' but make adjustments to 'len'.
> >
> > The logic is very confusing.
>
> Yes let me clarify a bit.
>
> In the code 'payload' is the exact NC-SI payload length, which goes into NC-SI packet header and needs to be actual unpadded payload length.
>
> 'len' is used to allocate total NC-SI packet buffer (include padding).
>
> The original calculation of 'len' was done by summing up NCSI header + payload + checksum, without taking into account of possible padding, e.g.
>
> len += sizeof(struct ncsi_cmd_pkt_hdr) + 4; /* 4 is the checksum size */
> if (nca->payload < 26)
> len += 26;
> else
> len += nca->payload;
> /* Allocate skb */
> skb = alloc_skb(len, GFP_ATOMIC);
>
> This works today for all standard NC-SI commands (in spec v1.1) because all standard commands have payload size < 26, and packet size is then set to minimum of 46 (16 hdr + 26 payload + 4 cksum) bytes.
>
> And mem clearing is done in each of the standard cmd handlers, e.g.
> ncsi_cmd_handler_sp, ncsi_cmd_handler_ae.
>
>
>
> The problem occurs if payload >= 26 and is unaligned. This could happen on some OEM commands, and I see this happening when we carry PLDM traffic over NC-SI packet.
> (PLDM header being 3 bytes and payload size can be large)
>
> The skb allocated would be too small, and later when checksum is calculated and written:
>
> pchecksum = (__be32 *)((void *)h + sizeof(struct ncsi_pkt_hdr) +
> ALIGN(nca->payload, 4));
> *pchecksum = htonl(checksum);
>
> Part of the checksum would fall outside of our allocated buffer.
>
> PLDM over NC-SI and OEM NC-SI commands are currently handled in
>
> @@ -213,17 +213,22 @@ static int ncsi_cmd_handler_oem(struct sk_buff *skb,
>
> So here I ensure the skb allocation takes padding into account, and do the initial mem clearing to set the padding bytes
>
> + 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);
>
> So in this patch I updated both standard command handler (in case future spec updates adds commands with payload >= 26) and OEM/generic command handler to support unaligned payload size.
>
> Regards,
> -Ben

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