Re: [kernel-hardening] Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM

From	Matt Brown <matt@nmatt.com>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM
Date	2017-06-04 14:50 +0200
Message-ID	<tOD8K-56m-9@gated-at.bofh.it> (permalink)
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On 06/04/2017 01:47 AM, Eric Biggers wrote:
> On Sun, Jun 04, 2017 at 01:24:13AM -0400, Matt Brown wrote:
>> On 06/03/2017 02:33 AM, Al Viro wrote:
>>> On Sat, Jun 03, 2017 at 01:53:51AM -0400, Matt Brown wrote:
>>>
>>>> +static int tpe_bprm_set_creds(struct linux_binprm *bprm)
>>>> +{
>>>> +	struct file *file = bprm->file;
>>>> +	struct inode *inode = d_backing_inode(file->f_path.dentry->d_parent);
>>>> +	struct inode *file_inode = d_backing_inode(file->f_path.dentry);
>>>
>>> Bloody wonderful.  Do tell, what *does* prevent a race with rename(2) here,
>>> somehow making sure that your 'inode' won't get freed right under you?
>>>
>>
>> Good catch. How does this look:
>>
>> spin_lock(&inode->i_lock);
>> spin_lock(&file_inode->i_lock);
>> if (global_nonroot(inode->i_uid) && !uid_eq(inode->i_uid, cred->uid))
>> 	reason1 = "directory not owned by user";
>> else if (inode->i_mode & 0002)
>> 	reason1 = "file in world-writable directory";
>> else if ((inode->i_mode & 0020) && global_nonroot_gid(inode->i_gid))
>> 	reason1 = "file in group-writable directory";
>> else if (file_inode->i_mode & 0002)
>> 	reason1 = "file is world-writable";
>> spin_unlock(&inode->i_lock);
>> spin_unlock(&file_inode->i_lock);
>>
>> and likewise for other places in the code?
>
> No, it needs to take a reference on the parent dentry before using it, using
> dget_parent(), I think, and then dropping it later with dput().  Taking i_lock
> isn't needed.
>
> Eric
>

Got it. Thank you!

Matt Brown

Thread

[PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM Matt Brown <matt@nmatt.com> - 2017-06-03 08:00 +0200
  Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-03 08:40 +0200
    Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM Matt Brown <matt@nmatt.com> - 2017-06-04 07:30 +0200
      Re: [kernel-hardening] Re: [PATCH v1 1/1] Add Trusted Path Execution  as a stackable LSM Eric Biggers <ebiggers3@gmail.com> - 2017-06-04 07:50 +0200
        Re: [kernel-hardening] Re: [PATCH v1 1/1] Add Trusted Path Execution  as a stackable LSM Matt Brown <matt@nmatt.com> - 2017-06-04 14:50 +0200
      Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-04 09:00 +0200
  Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a  stackable LSM Jann Horn <jannh@google.com> - 2017-06-03 12:40 +0200
    Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a  stackable LSM Matt Brown <matt@nmatt.com> - 2017-06-04 00:40 +0200
  Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a  stackable LSM Mickaël Salaün <mic@digikod.net> - 2017-06-04 18:50 +0200
    Re: [kernel-hardening] [PATCH v1 1/1] Add Trusted Path Execution as a  stackable LSM Mickaël Salaün <mic@digikod.net> - 2017-06-05 00:10 +0200

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