Bug#770492: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after permission checks
- To: James Morris <jmorris@namei.org>, Ben Hutchings <ben@decadent.org.uk>
- Cc: Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, 770492@bugs.debian.org, Ben Harris <bjh21@cam.ac.uk>, oss-security@lists.openwall.com, John Johansen <john.johansen@canonical.com>, Paul Moore <paul@paul-moore.com>, Casey Schaufler <casey@schaufler-ca.com>
- Subject: Bug#770492: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after permission checks
- From: Stephen Smalley <sds@tycho.nsa.gov>
- Date: Wed, 21 Jan 2015 09:03:35 -0500
- Message-id: <[🔎] 54BFB1B7.4020402@tycho.nsa.gov>
- Reply-to: Stephen Smalley <sds@tycho.nsa.gov>, 770492@bugs.debian.org
- In-reply-to: <[🔎] alpine.LRH.2.11.1501211014580.15885@namei.org>
- References: <[🔎] 1421537206.31046.74.camel@decadent.org.uk> <[🔎] alpine.LRH.2.11.1501211014580.15885@namei.org>
On 01/20/2015 06:17 PM, James Morris wrote:
> On Sat, 17 Jan 2015, Ben Hutchings wrote:
>
>> chown() and write() should clear all privilege attributes on
>> a file - setuid, setgid, setcap and any other extended
>> privilege attributes.
>>
>> However, any attributes beyond setuid and setgid are managed by the
>> LSM and not directly by the filesystem, so they cannot be set along
>> with the other attributes.
>>
>> Currently we call security_inode_killpriv() in notify_change(),
>> but in case of a chown() this is too early - we have not called
>> inode_change_ok() or made any filesystem-specific permission/sanity
>> checks.
>>
>> Add a new function setattr_killpriv() which calls
>> security_inode_killpriv() if necessary, and change the setattr()
>> implementation to call this in each filesystem that supports xattrs.
>> This assumes that extended privilege attributes are always stored in
>> xattrs.
>
> It'd be useful to get some input from LSM module maintainers on this.
>
> e.g. doesn't SELinux already handle this via policy directives?
There have been a couple postings of a similar patch set [1] by Jan
Kara, although I don't believe that series addressed chown().
If I am reading the patches correctly, they (correctly) don't affect
SELinux or Smack labels; they are just calling the existing
security_inode_killpriv() hook, which is only implemented for the
capability module to remove the security.capability xattr.
[1] http://marc.info/?l=linux-security-module&m=141890696325054&w=2
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