Date: Fri, 7 Dec 2018 19:47:57 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r341689 - in head: lib/libc/sys sys/compat/freebsd32 sys/kern sys/sys Message-ID: <20181207174757.GI52540@kib.kiev.ua> In-Reply-To: <e9e457ed-00f5-705e-55ea-1ad602f34ef0@FreeBSD.org> References: <201812071517.wB7FHTiI035911@repo.freebsd.org> <e9e457ed-00f5-705e-55ea-1ad602f34ef0@FreeBSD.org>
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On Fri, Dec 07, 2018 at 09:21:34AM -0800, John Baldwin wrote: > On 12/7/18 7:17 AM, Konstantin Belousov wrote: > > Author: kib > > Date: Fri Dec 7 15:17:29 2018 > > New Revision: 341689 > > URL: https://svnweb.freebsd.org/changeset/base/341689 > > > > Log: > > Add new file handle system calls. > > > > Namely, getfhat(2), fhlink(2), fhlinkat(2), fhreadlink(2). The > > syscalls are provided for a NFS userspace server (nfs-ganesha). > > > > Submitted by: Jack Halford <jack@gandi.net> > > Sponsored by: Gandi.net > > Tested by: pho > > Feedback from: brooks, markj > > MFC after: 1 week > > Differential revision: https://reviews.freebsd.org/D18359 > > Can this be used to implement 'flink' (create a link to an open file > descriptor)? Hmm, it appears so. It is limited to PRIV_VFS_GETFH at least. > The getfh(2) manpage notes this explicitly, but the new manpages don't > appear to. Even with the PRIV check, I'm still somewhat nervous about what > flink means for processes running as root that are using Capsicum. Maybe > it's ok, but I didn't see any discussion of this in the review. If the process can execute getfh(2) and fhlink(2), then its privileges are not much different from the privileges of the in-kernel NFS server. During the review, I verified that PRIV_VFS_GETFH is checked, and considered suggesting fine-grainer individual privs for other operations, but decided that this is not too useful. That said, how can you translate from file descriptor to file handle ? E.g. to know (and not guess) the file handle on UFS, the process must posses PRIV_VFS_GENERATION. If you have PRIV_VFS_GETFH/PRIV_VFS_GENERATION privs, then you can implement flink(2) for UFS, but might be that it is even not undesirable.
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