From: "J. Bruce Fields" Subject: Re: [PATCH] bug in read_buf Date: Tue, 20 Apr 2010 15:39:44 -0400 Message-ID: <20100420193944.GB31901@fieldses.org> References: <19405.3732.562014.510508@notabene.brown> <20100420165152.GD28826@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: Neil Brown , linux-nfs@vger.kernel.org To: "William A. (Andy) Adamson" Return-path: Received: from fieldses.org ([174.143.236.118]:53134 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754264Ab0DTTjq (ORCPT ); Tue, 20 Apr 2010 15:39:46 -0400 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Apr 20, 2010 at 03:24:59PM -0400, William A. (Andy) Adamson wro= te: > On Tue, Apr 20, 2010 at 12:51 PM, J. Bruce Fields wrote: > > On Tue, Apr 20, 2010 at 12:16:52PM +1000, Neil Brown wrote: > >> > >> Surely this can never have worked... which implies that the code h= as > >> never been used? > >> > >> When read_buf is called to move over to the next page in the pagel= ist > >> of an NFSv4 request, it sets argp->end to essentially a random > >> number, certainly not an address within the page which argp->p now > >> points to. =C2=A0So subsequent calls to READ_BUF will think there = is much > >> more than a page of spare space (the cast to u32 ensures an unsign= ed > >> comparison) so we can expect to fall off the end of the second > >> page. > > > > Yipes, thanks. > > > >> I guess we never ever receive requests with any operation starting > >> beyond the first page! > > > > putfh-write-getattr, for example, is common enough. =C2=A0The write= decoding > > should leave arg->end set correctly. =C2=A0But there are two read_b= uf()'s in > > decode_getattr(), and I can't see why we don't hit this bug on a wr= ite > > that leaves that final getattr exactly straddling a page boundary. >=20 > The write data is dumped into the rq_vec which has non-contiguous > pages. So the xdr_buf head only holds the putfh result, the short > write response header (v4 stateid, offset, how, length, etc), and the= n > the getattr. so there is plenty of space. This is the server-side write-decoding, so you could see: rpc header | putfh | write ... data ... | getattr ^ | page boundary here --b. >=20 > -->Andy >=20 > > > > --b. > > > >> [[ > >> I found this while looking at why fsstress over NFS over RDMA caus= ed > >> a bad memory dereference in READ32, suggesting that 'p' had a bad > >> value. =C2=A0However it was ffff8801299188f0, which is not an "I'v= e fallen > >> off the end of the page" sort of value. =C2=A0So I think it must b= e a > >> different bug :-( =C2=A0It is as if the page is being unmapped und= erneath > >> us... > >> ]] > >> NeilBrown > >> > >> > >> > >> > >> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c > >> index e170317..34ccf81 100644 > >> --- a/fs/nfsd/nfs4xdr.c > >> +++ b/fs/nfsd/nfs4xdr.c > >> @@ -161,10 +161,10 @@ static __be32 *read_buf(struct nfsd4_compoun= dargs *argp, u32 nbytes) > >> =C2=A0 =C2=A0 =C2=A0 argp->p =3D page_address(argp->pagelist[0]); > >> =C2=A0 =C2=A0 =C2=A0 argp->pagelist++; > >> =C2=A0 =C2=A0 =C2=A0 if (argp->pagelen < PAGE_SIZE) { > >> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D p + (arg= p->pagelen>>2); > >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D argp->p = + (argp->pagelen>>2); > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->pagelen =3D= 0; > >> =C2=A0 =C2=A0 =C2=A0 } else { > >> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D p + (PAG= E_SIZE>>2); > >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D argp->p = + (PAGE_SIZE>>2); > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->pagelen -=3D= PAGE_SIZE; > >> =C2=A0 =C2=A0 =C2=A0 } > >> =C2=A0 =C2=A0 =C2=A0 memcpy(((char*)p)+avail, argp->p, (nbytes - a= vail)); > >> @@ -1426,10 +1426,10 @@ nfsd4_decode_compound(struct nfsd4_compoun= dargs *argp) > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 argp->p =3D page_address(argp->pagelist[0]); > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 argp->pagelist++; > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 if (argp->pagelen < PAGE_SIZE) { > >> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D p + (argp->pagelen>>2); > >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D argp->p + (argp->pagelen>= >2); > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->pagelen =3D 0; > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 } else { > >> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D p + (PAGE_SIZE>>2); > >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->end =3D argp->p + (PAGE_SIZE>>2); > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 argp->pagelen -=3D PAGE_SIZE; > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 } > >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 } > >> > >> > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-nfs= " in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at =C2=A0http://vger.kernel.org/majordomo-info.= html > >