On 04/09/2014 01:10 AM, Vlad Yasevich wrote: > On 04/08/2014 06:23 PM, Daniel Borkmann wrote: >> In function sctp_wake_up_waiters() we need to involve a test >> if the association is declared dead. If so, we don't have any >> reference to a possible sibling association anymore and need >> to invoke sctp_write_space() instead and normally walk the >> socket's associations and notify them of new wmem space. The >> reason for special casing is that, otherwise, we could run >> into the following issue: >> >> sctp_association_free() >> `-> list_del(&asoc->asocs) <-- poisons list pointer >> asoc->base.dead = true >> sctp_outq_free(&asoc->outqueue) >> `-> __sctp_outq_teardown() >> `-> sctp_chunk_free() >> `-> consume_skb() >> `-> sctp_wfree() >> `-> sctp_wake_up_waiters() <-- dereferences poisoned pointers >> if asoc->ep->sndbuf_policy=0 >> >> Therefore, only walk the list in an 'optimized' way if we find >> that the current association is still active. It's also more >> clean in that context to just use list_del_init() when we call >> sctp_association_free(). Stress-testing seems fine now. > > One of the reasons that we don't use list_del_init() here is that > we want to be able to trap on uninitialized/corrupt list manipulation, > just like you did. If it wasn't there, the bug would have been hidden. > > Please keep it there. The rest of the patch is fine. Test run over night and I've seen no issues. But I'd still question the usage of asoc->base.dead though, I think this approach of testing for asoc->base.dead is a bit racy (perhaps general usage of it, imho) - at least here there's a tiny window where we poison pointers before we actually declare the associaton dead. Also, I think even if we would have deleted ourselves from the list after declaring the association dead, a different CPU accessing this association via sctp_wfree() might already have gotten past the asoc->base.dead test while we declare it dead in the meantime. Imho, this still needs to be resolved differently. I'll look further ... -- 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
