On Tue, Apr 18, 2017 at 01:13:51PM -0400, J. Bruce Fields wrote: > On Tue, Apr 18, 2017 at 10:25:20AM +1000, NeilBrown wrote: > > I can't say that I like this patch at all. > > > > The problem is that: > > > > pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply. > > * We assume one is at most one page > > */ > > > > this assumption is never verified. > > To my mind, the "obvious" way to verify this assumption is that an > > attempt to generate a multi-page reply should fail if there was a > > multi-page request. > > A third option, by the way, which Ari Kauppi argued for, is adding a > null check each time we increment rq_next_page, since we seem to arrange > for the page array to always be NULL-terminated. > > > Failing if there was a little bit of extra noise at the end of the > > request seems harsher than necessary, and could result in a regression. > > You're worrying there might be a weird old client out there somewhere? > I guess it seems like a small enough risk to me. I'm more worried the > extra garbage might violate assumptions elsewhere in the code. > > But, this looks good too: But, I'm not too happy about putting that NFSv2/v3-specific check in common rpc code. Also, I think this check comes too late for some of the damage. I may go with some variation on Ari's idea, let me give it a try.... --b. > > > We already know how big replies can get, so we can perform a complete > > sanity check quite early: > > > > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c > > index a08aeb56b8e4..14f4d425cf8c 100644 > > --- a/net/sunrpc/svc.c > > +++ b/net/sunrpc/svc.c > > @@ -1196,6 +1196,12 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv) > > goto err_bad_proc; > > rqstp->rq_procinfo = procp; > > > > + if ((procp->pc_xdrressize == 0 || > > + procp->pc_xdrressize > XDR_QUADLEN(PAGE_SIZE)) && > > + rqstp->rq_arg.len > PAGE_SIZE) > > + /* The assumption about request/reply sizes in svc_init_buffer() is violated! */ > > + goto err_garbage; > > + > > /* Syntactic check complete */ > > serv->sv_stats->rpccnt++; > > > > > > I haven't tested this at all and haven't even convinced myself that > > it covers every case (though I cannot immediately think of any likely > > corners). > > > > Does it address your test case? > > I'll check, it probably does. > > We'd need to limit the test to v2/v3. > > I'm also not opposed to doing both (or all three). > > --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
