linux-kernel - Re: [PATCH] fuse: add missing iput() in fuse

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Message-ID: <20251219221426.GA1712166@ZenIV>
Date: Fri, 19 Dec 2025 22:14:26 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Luis Henriques <luis@...lia.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, mszeredi@...e.cz,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com
Subject: Re: [PATCH] fuse: add missing iput() in fuse_lookup() error path

On Fri, Dec 19, 2025 at 10:10:31PM +0000, Al Viro wrote:
> On Fri, Dec 19, 2025 at 05:43:09PM +0000, Luis Henriques wrote:
> > The inode use count needs to be dropped in the fuse_lookup() error path,
> > when there's an error returned by d_splice_alias().
> > 
> > (While there, remove extra white spaces before labels.)
> > 
> > Fixes: 5835f3390e35 ("fuse: use d_materialise_unique()")
> > Signed-off-by: Luis Henriques <luis@...lia.com>
> 
> Have you actually looked at d_splice_alias()?
> 
> It does consume inode reference in all cases, success or error.  On success
> it gets transferred to dentry; on failure it is dropped.  That's quite
> deliberate, since it makes life much simplier for failure handling in the
> callers.
> 
> If you can reproduce a leak there, I would like to see a reproducer.
> If not, I would say that your patch introduces a double-iput.
> 
> NAK.

PS: out_iput in there is needed only on one failure exit - after we'd
found an inode and before we'd passed it to d_splice_alias().

FWIW, I would rather replace that with
	if (inode && get_node_id(inode) == FUSE_ROOT_ID) {
		iput(inode);
		return ERR_PTR(-EIO);
	}
and turned all goto out_err; into direct returns.