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Subject: Re: [PATCH -next] fs: Fix memory leaks in do_renameat2() error paths
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Qian Cai <cai@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20201030152407.43598-1-cai@redhat.com>
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 <ad9357e9-8364-a316-392d-7504af614cac@kernel.dk>
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 <d858ba48-624f-43be-93cf-07d94f0ebefd@kernel.dk>
 <20201030222213.GR3576660@ZenIV.linux.org.uk>
 <a1e17902-a204-f03d-2a51-469633eca751@kernel.dk>
 <87eelba7ai.fsf@x220.int.ebiederm.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <f33a6b5e-ecc9-2bef-ab40-6bd8cc2030c2@kernel.dk>
Date:   Mon, 2 Nov 2020 12:54:40 -0700
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On 11/2/20 12:27 PM, Eric W. Biederman wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>> On 10/30/20 4:22 PM, Al Viro wrote:
>>> On Fri, Oct 30, 2020 at 02:33:11PM -0600, Jens Axboe wrote:
>>>> On 10/30/20 12:49 PM, Al Viro wrote:
>>>>> On Fri, Oct 30, 2020 at 12:46:26PM -0600, Jens Axboe wrote:
>>>>>
>>>>>> See other reply, it's being posted soon, just haven't gotten there yet
>>>>>> and it wasn't ready.
>>>>>>
>>>>>> It's a prep patch so we can call do_renameat2 and pass in a filename
>>>>>> instead. The intent is not to have any functional changes in that prep
>>>>>> patch. But once we can pass in filenames instead of user pointers, it's
>>>>>> usable from io_uring.
>>>>>
>>>>> You do realize that pathname resolution is *NOT* offloadable to helper
>>>>> threads, I hope...
>>>>
>>>> How so? If we have all the necessary context assigned, what's preventing
>>>> it from working?
>>>
>>> Semantics of /proc/self/..., for starters (and things like /proc/mounts, etc.
>>> *do* pass through that, /dev/stdin included)
>>
>> Don't we just need ->thread_pid for that to work?
> 
> No.  You need ->signal.
> 
> You need ->signal->pids[PIDTYPE_TGID].  It is only for /proc/thread-self
> that ->thread_pid is needed.
> 
> Even more so than ->thread_pid, it is a kernel invariant that ->signal
> does not change.

I don't care about the pid itself, my suggestion was to assign ->thread_pid
over the lookup operation to ensure that /proc/self/ worked the way that
you'd expect.

-- 
Jens Axboe