Bugtraq mailing list archives
Re: nfs handles/lifetime
From: casper () Holland Sun COM (Casper Dik)
Date: Wed, 10 May 1995 16:25:52 +0200
Since an NFS filehandle is derived from the inode characteristics, it never changes, except when an admin uses fsirand. Now, since all access checking is done with mountd, won't an exported system still be available for access if you have its old filehandle even though the admin takes its entry out of /etc/exports? For instance, let's say A is a server, and B is its client. A exports /usr to B. B mounts A:/usr and writes down the filehandle. A decides to stop exporting /usr and removes it from the exports file. Can B still access files in /usr? I did strings(1) on various vendors' nfsds, and found that about half of them had /etc/exports in them. Can anyone elaborate on this?
Since I'm only familiar with Sun's implementation, I can only comment on that implementation. In Sun's implementation, the kernel keeps a list of export mount points. A file handle is a combination of ( <disk id>, <export point id>, <file id>) If an exported filesystem is no longer exported, the <export point id> is removed from the kernel export list. Each NFS access checks the <export point id> for validity, so references to files under that directory will yield "Stale NFS filehandle" In short: if you unexport a filesystem, it can no longer be accessed. However, if you change the export list (e.g., make it more restrictive) all clients that have filehandles will keep them and can continue to use them. /etc/exports is merely a reflection of which file are exported, it is not used by nfsd, as far as I know. The mount info is kept in mountd and inside the kernel. The strings "/etc/exports" is part of libc, so systems that ship a statically linked nfsd, e.g., because they don't support dynamic linking, will show the strings "/etc/exports". Casper
Current thread:
- Re: and now, back to your regularly scheduled discussion topic... Patrick Horgan (May 07)
- nfs handles/lifetime Nathan Lawson (May 08)
- Re: nfs handles/lifetime Casper Dik (May 10)
- Re: and now, back to your regularly scheduled discussion topic... Philip Guenther (May 08)
- Re: and now, back to your regularly scheduled discussion topic... C. Harald Koch (May 09)
- <Possible follow-ups>
- Re: and now, back to your regularly scheduled discussion topic... robert owen thomas (May 08)
- nfs handles/lifetime Nathan Lawson (May 08)