Re: [patch 7/8] allow unprivileged mounts
- From: ebiederm@xxxxxxxxxxxx (Eric W. Biederman)
- Date: Sat, 21 Apr 2007 15:33:25 -0600
Andi Kleen <andi@xxxxxxxxxxxxxx> writes:
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
On Fri, 20 Apr 2007 12:25:39 +0200 Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
Define a new fs flag FS_SAFE, which denotes, that unprivileged
mounting of this filesystem may not constitute a security problem.
Since most filesystems haven't been designed with unprivileged
mounting in mind, a thorough audit is needed before setting this flag.
Practically speaking, is there any realistic likelihood that any filesystem
apart from FUSE will ever use this?
If it worked for mount --bind for any fs I could see uses of this. I haven't
thought
through the security implications though, so it might not work.
Binding a directory that you have access to in other was is essentially
the same thing as a symlink. So there are no real security implications
there. The only problem case I can think of is removal media that you
want to remove but someone has made a bind mount to. But that is
essentially the same case as opening a file so there are no new
real issues. Although our diagnostic tools will likely fall behind
for a bit.
We handle the security implications by assigning an owner to all mounts
and only allowing you to add additional mounts on top of a mount you
already own.
If you have the right capabilities you can create a mount owned by
another user.
For a new mount if you don't have the appropriate capabilities nodev
and nosuid will be forced.
Initial super block creation is a lot more delicate so we need the
FS_SAFE flag, to know that the kernel is prepared to deal with the
crazy things that a hostile user space is prepared to do.
Eric
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- References:
- [patch 0/8] mount ownership and unprivileged mount syscall (v4)
- From: Miklos Szeredi
- [patch 7/8] allow unprivileged mounts
- From: Miklos Szeredi
- Re: [patch 7/8] allow unprivileged mounts
- From: Andrew Morton
- Re: [patch 7/8] allow unprivileged mounts
- From: Andi Kleen
- [patch 0/8] mount ownership and unprivileged mount syscall (v4)
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