linux-kernel - Re: [PATCH] ubifs: Fix O_TMPFILE corner case in ubifs

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Date:   Thu, 30 Mar 2017 13:35:06 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        linux-mtd@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Artem Bityutskiy <dedekind1@...il.com>,
        "stable [v4.9]" <stable@...r.kernel.org>,
        Ralph Sennhauser <ralph.sennhauser@...il.com>
Subject: Re: [PATCH] ubifs: Fix O_TMPFILE corner case in ubifs_link()

On Thu, Mar 30, 2017 at 1:23 PM, Richard Weinberger <richard@....at> wrote:
> Am 30.03.2017 um 11:49 schrieb Richard Weinberger:
>> Am 30.03.2017 um 11:32 schrieb Adrian Hunter:
>>>> diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
>>>> index 0858213a4e63..0139155045fe 100644
>>>> --- a/fs/ubifs/dir.c
>>>> +++ b/fs/ubifs/dir.c
>>>> @@ -748,6 +748,11 @@ static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
>>>>             goto out_fname;
>>>>
>>>>     lock_2_inodes(dir, inode);
>>>> +
>>>> +   /* Handle O_TMPFILE corner case, it is allowed to link a O_TMPFILE. */
>>>> +   if (inode->i_nlink == 0)
>>>> +           ubifs_delete_orphan(c, inode->i_ino);
>>>
>>> Isn't there also a deletion inode in the journal?  If the recovery sees that
>>> won't it delete the file data?
>>
>> Yes, but ubifs_link() adds a new journal entry which revives the inode.
>> This should cancel out the deletion, right?
>> You know the UBIFS journal better than I do. :-)
>
> Reading deeper into the proved that I was wrong.
> AFAIKT UBIFS' journal has currently no way to revive a deleted inode.
> So, we have to think about a new solution.
>

Not that I know anything about ubifs, but why do you need the deleted
inode record in the first place for an O_TMPFILE.
vfs ensures you that you can only link back an O_TMPFILE, not a deleted
inode.

It does not appear to be the right thing to do to pass deletion=1 to
ubifs_jnl_update(), but deletion=0 doesn't look right as well..