linux-kernel - Re: [PATCH] xfs: fix a NULL pointer problem

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Date: Thu, 20 Jun 2024 01:09:08 -0700
From: Christoph Hellwig <hch@...radead.org>
To: shaozongfan <shaozongfan@...inos.cn>
Cc: chandan.babu@...cle.com, djwong@...nel.org, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: fix a NULL pointer problem

On Thu, Jun 20, 2024 at 03:43:13PM +0800, shaozongfan wrote:
> when a process using getdents64() api to get a Folder inside
> the file directory,meantime other process delete the file
> directory.it would cause an error like this:

Can you share your reproducer?

>  	if (ctx->pos <= dotdot_offset) {
> -		ino = xfs_dir2_sf_get_parent_ino(sfp);
> +		sfp1 = sfp;
> +		if (sfp1 == NULL)
> +			return 0;
> +		ino = xfs_dir2_sf_get_parent_ino(sfp1);

This looks ... odd.  Assigning one pointer variable to another
doesn't revalidate anything.  And xfs_dir2_sf_getdents is called
with the iolock held, which should prevent xfs_idestroy_fork
from racing with it.  And if for some reason it doesn't we need
to fix the synchronization.