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Message-ID: <46AF4034.6080507@RedHat.com>
Date: Tue, 31 Jul 2007 09:59:16 -0400
From: Steve Dickson <SteveD@...hat.com>
To: Stefan Walter <stefan.walter@....ethz.ch>
CC: linux-kernel@...r.kernel.org
Subject: Re: rpc.mountd crashes when extensively using netgroups
Stefan Walter wrote:
>
> We do this on a much larger scale though. The bug we ran into is
> in line 96 in utils/mountd/auth.c. The strcpy can corrupt
> memory when it copies the string returned by client_compose() to
> my_client.m_hostname which has a fixed size of 1024 bytes.
> For our example above, client_compose() returns "@joe,@jane"
> for any machine in the offices_1 netgroup. Unfortunately we have
> a machine to which roughly 150 netgroups like @joe or @jane
> export to and client_compose() returns a string over 1300 bytes
> long and rpc.mountd nicely segfaults.
>
> To prevent the crash is of course trivial: Inserting a simple
> 'if (strlen(n) > 1024) return NULL;' before line 96 does the job.
Does the attached patch help?
>
> There are however two issues for which we could not find an easy
> solution:
>
> 1. For every client rpc.mountd and the kernel seem to exchange
> and use lists with _all_ netgroups used in exports that are
> relevant for granting permission to some share for a particular
> client. We could imagine two optimizations here:
>
> * Resolve netgroups and only put the (member) netgroups that
> contained the host name that would be used to authorize
> a mount in the list.
>
> * Use the list of mounted paths per client and only put the
> netgroup(s) used to export paths that are actually mounted
> on a client.
These sound reasonable...
>
> 2. Using a fixed size for NFSCLNT_IDMAX does not scale. Mounting
> shares on a client for which the 'if' clause of the quick fix
> becomes true will not be possible. We thought about enlarging
> NFSCLNT_IDMAX and using a custom kernel but dropped the idea.
True...
>
> Our ultimate goal is to get Red Hat fix the code in nfs-utils 1.0.6
> that is used in RHEL4. A first step would be to get a suitable fix in
> the current nfs-utils.
Please open up bugs on all three of these issues and
we'll see what can done...
steved.
View attachment "mountd-netgroup.patch" of type "text/x-patch" (764 bytes)
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