From: Trond Myklebust Subject: Re: Memory corruption in nfs3_xdr_setaclargs() Date: Tue, 20 Jan 2009 13:15:01 -0500 Message-ID: <1232475301.7055.14.camel@heimdal.trondhjem.org> References: <49760685.4030409@redhat.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-nfs@vger.kernel.org To: "Sachin S. Prabhu" Return-path: Received: from mail-out2.uio.no ([129.240.10.58]:47038 "EHLO mail-out2.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180AbZATSPH (ORCPT ); Tue, 20 Jan 2009 13:15:07 -0500 In-Reply-To: <49760685.4030409@redhat.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 2009-01-20 at 17:14 +0000, Sachin S. Prabhu wrote: > A mistake in calculating the space left in the header in nfs3_xdr_setaclargs() > can cause memory corruption when setting a large number of acls. > > Reproducer: > > On Server: > 1) Create directory /test and set mode 777. > mkdir /test; chmod 777 /test > 2) Add 200 users and set default acl for user on /test > for i in {1..200}; do echo $i; useradd user$i; setfacl -m d:u:user$i:rwx > /test;done > 3) Add export /test in /etc/exports > /test *(rw) > > On client > 1) Mount server:/test > mount server:/test /mnt > 2) Create large number of directories on the the share. > cd/mnt; for i in {1..1000}; do mkdir $i; done > At this point, the client should crash. > > A change in call_header changes the value req->rq_snd_buf->head[0]->iov_len to > reflect the exact size of the header. > [PATCH] RPC: Ensure XDR iovec length is initialized correctly in call_header > 334ccfd545bba9690515f2c5c167d5adb161989b > > The iov_len is set to the size of the header in call_header(). > req->rq_slen = xdr_adjust_iovec(&req->rq_svec[0], p); > > nfs3_xdr_setaclargs() depends on the older behavior and uses this value when > calculating the number of ACLs it can fit into the header. > > /* put as much of the acls into head as possible. */ > len_in_head = min_t(unsigned int, buf->head->iov_len - base, len); > len -= len_in_head; > req->rq_slen = xdr_adjust_iovec(req->rq_svec, p + (len_in_head >> 2)); > > Since at this stage, iov_len < base, len_in_head will always be set to len. For > a large number of ACLs, this will end up over-writing other parts of memory on > the nfs client. > > The following patch which set len_in_head to 0 was tested with the reproducer > and was found to fix the problem. > Looks alright. Could you please add a s-o-b line? Cheers Trond > --- fs/nfs/nfs3xdr.c.orig 2009-01-20 15:18:12.000000000 +0000 > +++ fs/nfs/nfs3xdr.c 2009-01-20 15:33:45.000000000 +0000 > @@ -691,7 +691,10 @@ nfs3_xdr_setaclargs(struct rpc_rqst *req > *p++ = htonl(args->mask); > base = (char *)p - (char *)buf->head->iov_base; > /* put as much of the acls into head as possible. */ > - len_in_head = min_t(unsigned int, buf->head->iov_len - base, len); > + if ( buf->head->iov_len > base ) > + len_in_head = min_t(unsigned int, buf->head->iov_len - base, len); > + else > + len_in_head = 0; > len -= len_in_head; > req->rq_slen = xdr_adjust_iovec(req->rq_svec, p + (len_in_head >> 2)); > > Thanks to Kevin Rudd who did the major legwork here to figure the problem and > create the patch. > > Sachin Prabhu >