From: Vladislav Yasevich <vladislav.yasevich@xxxxxx> Date: Fri, 18 Feb 2011 09:43:30 -0500 > On 02/18/2011 07:01 AM, Jiri Bohac wrote: >> On Fri, Feb 18, 2011 at 07:26:18PM +0800, Shan Wei wrote: >>> Jiri Bohac wrote, at 02/18/2011 07:12 AM: >>>> commit 5fa782c2f5ef6c2e4f04d3e228412c9b4a4c8809 re-worked the >>>> handling of unknown parameters. sctp_init_cause_fixed() can now >>>> return -ENOSPC if there is not enough tailroom in the error >>>> chunk skb. When this happens, the error header is not appended to >>>> the error chunk. In that case, the payload of the unknown parameter >>>> should not be appended either. >>>> >>>> Signed-off-by: Jiri Bohac <jbohac@xxxxxxx> >>> >>> For this case, there is no more tailroom in skb >> >> not always true: >> >> both sctp_init_cause_fixed() and sctp_addto_chunk_fixed() get >> passesd WORD_ROUND(ntohs(param.p->length) as the paylen/len >> parameter. >> >> sctp_init_cause_fixed() does: >> len = sizeof(sctp_errhdr_t) + paylen; >> if (skb_tailroom(chunk->skb) < len) >> return -ENOSPC; >> >> if paylen is only slightly smaller than the tailroom (by less >> than sizeof(sctp_errhdr_t) bytes), -ENOSPEC will be returned and >> the header will not be appended to the error chunk. >> >> But later sctp_addto_chunk_fixed() does this check: >> if (skb_tailroom(chunk->skb) >= len) >> which will pass and the unknown parameter value will be appended >> to the error chunk without the error header. >> >>> we send incomplete INIT-ACK chunk. With your patch, this chunk also >>> can't info the sender of INIT Chunk which parameter is not unrecognized. >>> So maybe this handle is not perfect. >> >> The logic of not reporting unknown parameters for which we don't >> have space in the pre-allocated buffer remains unchanged. >> > > > Hi Jiri > > I agree. Good catch. If we can not add the error header to that packet, then we definitely > should not be adding the error payload either. > > We also don't want to abort as Shan Wei suggested. It is allowed, when exceeding the MTU to > drop errors that would not otherwise fit into the packet. It just may so happen that we > can report subsequent unknown parameters, but not this one in particular. > > Acked-by: Vlad Yasevich <vladislav.yasevich@xxxxxx> Applied, thanks everyone. -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
