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List:       linux-kernel
Subject:    Re: Possible permissions bug on NFSv3 kernel client
From:       Trond Myklebust <trond.myklebust () fys ! uio ! no>
Date:       2004-04-30 20:39:57
Message-ID: 1083357597.13656.37.camel () lade ! trondhjem ! org
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On Fri, 2004-04-30 at 16:17, Pascal Schmidt wrote:
> Then it's at least inconsistent with local filesystem behaviour. fsck
> has no problem opening device nodes for writing on my root filesystem
> even though it is mounted read-only at that point.

So why do you think that is inconsistent with my statement: "the
permissions checking has to be done by the server, period"?

The read-only mount option is a *local* override of the write
permissions on the server. It applies to regular files, directories, and
soft links *only*.
The read-only mount option does *not apply* to char/block devices such
as /dev/hd[a-z]*, /dev/tty*. Permission checks on open() for those
devices are done on the server *only* via the ACCESS rpc call.

This should be entirely consistent with local file behaviour.
Particularly since the code to deal with the read-only mount option in
nfs_permission() was pretty much cut-n-pasted from vfs_permission().

Cheers,
  Trond
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