linux-kernel - Re: [PATCH v2] proc: Allow pid_revalidate() during LOOKUP

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Date:   Mon, 14 Dec 2020 10:45:43 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Matthew Wilcox <willy@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>
Cc:     Stephen Brennan <stephen.s.brennan@...cle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v2] proc: Allow pid_revalidate() during LOOKUP_RCU

On 12/13/2020 8:29 AM, Matthew Wilcox wrote:
> On Sun, Dec 13, 2020 at 08:22:32AM -0600, Eric W. Biederman wrote:
>> Matthew Wilcox <willy@...radead.org> writes:
>>
>>> On Thu, Dec 03, 2020 at 04:02:12PM -0800, Stephen Brennan wrote:
>>>> -void pid_update_inode(struct task_struct *task, struct inode *inode)
>>>> +static int do_pid_update_inode(struct task_struct *task, struct inode *inode,
>>>> +			       unsigned int flags)
>>> I'm really nitpicking here, but this function only _updates_ the inode
>>> if flags says it should.  So I was thinking something like this
>>> (compile tested only).
>>>
>>> I'd really appreocate feedback from someone like Casey or Stephen on
>>> what they need for their security modules.
>> Just so we don't have security module questions confusing things
>> can we please make this a 2 patch series?  With the first
>> patch removing security_task_to_inode?
>>
>> The justification for the removal is that all security_task_to_inode
>> appears to care about is the file type bits in inode->i_mode.  Something
>> that never changes.  Having this in a separate patch would make that
>> logical change easier to verify.
> I don't think that's right, which is why I keep asking Stephen & Casey
> for their thoughts.  For example,
>
>  * Sets the smack pointer in the inode security blob
>  */
> static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
> {
>         struct inode_smack *isp = smack_inode(inode);
>         struct smack_known *skp = smk_of_task_struct(p);
>
>         isp->smk_inode = skp;
>         isp->smk_flags |= SMK_INODE_INSTANT;
> }
>
> That seems to do rather more than checking the file type bits.

I'm going to have to bring myself up to speed on the
discussion before I say anything dumb. I'm supposed to
be Not! Working! today. I will get on it as permitted.