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Date:   Mon, 12 Aug 2019 04:03:54 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     linux-fsdevel@vger.kernel.org,
        "J. Bruce Fields" <bfields@redhat.com>,
        syzbot <syzbot+2c95195d5d433f6ed6cb@syzkaller.appspotmail.com>
Subject: Re: [PATCH] nfsd: fix dentry leak upon mkdir failure.
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On Mon, Aug 12, 2019 at 11:16:11AM +0900, Tetsuo Handa wrote:
> syzbot is reporting that nfsd_mkdir() forgot to remove dentry created by
> d_alloc_name() when __nfsd_mkdir() failed (due to memory allocation fault
> injection) [1].

That's not the only problem I see there.
        ret = __nfsd_mkdir(d_inode(parent), dentry, S_IFDIR | 0600);
        if (ret)
                goto out_err;
        if (ncl) {
                d_inode(dentry)->i_private = ncl;
                kref_get(&ncl->cl_ref);
        }
and we are doing that to inode *after* it has become visible via dcache -
__nfsd_mkdir() has already done d_add() (and pinged f-snotify, at that).
Looks fishy...