Bugtraq mailing list archives
Re: /proc filesystem allows bypassing directory permissions on Linux
From: "Kinzel, David" <dakinzel () suncor com>
Date: Mon, 26 Oct 2009 15:27:15 -0600
-----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 LinuxI do not think mounting /proc should change access controlsemantics.It didn't in fact change anything. If the guest createdhardlink 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 directory is locked down to user-only permissions. You will be allowed access to whatever the file allows, despite what the directory permissions are. This seems expected to me, since the files will be the same inode. If I'm following 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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Current thread:
- Re: /proc filesystem allows bypassing directory permissions on Linux, (continued)
- Re: /proc filesystem allows bypassing directory permissions on Linux Pavel Kankovsky (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux Tony Finch (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux Matthew Dempsky (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux Tony Finch (Oct 27)
- Re: /proc filesystem allows bypassing directory permissions on Linux Matthew Dempsky (Oct 28)
- Re: /proc filesystem allows bypassing directory permissions on Linux psz (Oct 28)
- Re: /proc filesystem allows bypassing directory permissions on Linux Glynn Clements (Oct 29)
- Re: /proc filesystem allows bypassing directory permissions on Linux Matthew Dempsky (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux psz (Oct 27)
- Re: /proc filesystem allows bypassing directory permissions on Linux Pavel Machek (Oct 27)
- Re: /proc filesystem allows bypassing directory permissions on Linux Kinzel, David (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux Dan Yefimov (Oct 26)
- Re: /proc filesystem allows bypassing directory permissions on Linux Dan Yefimov (Oct 27)