Re: /proc filesystem allows bypassing directory permissions on L
> -----Original Message-----
> From: nomail@nomail.com [mailto:nomail@nomail.com]
> Sent: Monday, October 26, 2009 9:15 AM
> To: bugtraq@securityfocus.com
> Subject: Re: Re: /proc filesystem allows bypassing directory
> permissions on Linux
>
> >> I do not think mounting /proc should change access control
> semantics.
> >>
> >It didn't in fact change anything. If the guest created
> hardlink to that file in a unrestricted location, what would you say?
>
> Do your homework and test it. You can't create the hardlink -
> the link(oldpath, newpath) call will fail with EACCES if
> search permission is denied for any directory in oldpath or
> newpath. Documented in the manpage, and I just tested and verified it.
>
It's creating the hardlink (or setting the fd in /proc) before the director=
y is locked down to user-only permissions. You will be allowed access to wh=
atever the file allows, despite what the directory permissions are. This se=
ems expected to me, since the files will be the same inode. If I'm followin=
g this correctly it comes down to some distributions treating /proc/*/fd/* =
as hardlinks, for whatever reason.
>
> Fact is, directory permissions are relevant in Unix. Despite
> it's permissions, under the Unix access permission semantics
> the file is unwriteable for anyone but the owner, and this
> bug pokes a hole into that.
>
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