Messages in this thread |  | | From | <> | Subject | RE: [PATCH net-next] net/ncsi: support unaligned payload size in NC-SI cmd handler | Date | Tue, 3 Sep 2019 19:21:07 +0000 |
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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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