linux-kernel - Re: [PATCH] ovl: Fix PTR

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Message-ID: <CAOQ4uxjU+RC_8Ec62irOy-Kd7H6UGuqpasq1qb5fXmZgkj_tUg@mail.gmail.com>
Date: Mon, 19 May 2025 08:43:16 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Charles Han <hanchunchao@...pur.com>
Cc: miklos@...redi.hu, linux-kernel@...r.kernel.org, 
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] ovl: Fix PTR_ERR zero argument warning

On Mon, May 19, 2025 at 6:11 AM Charles Han <hanchunchao@...pur.com> wrote:
>
> In the ovl_check_origin()  and ovl_index_upper()function, the
> PTR_ERR function was potentially passed a null pointer.
> To fix this issue, separated the null pointer check and the error
> pointer check, ensuring that PTR_ERR is only called with a valid
> error pointer.
>
> Fix below smatch warning.
> smatch warnings:
> fs/overlayfs/namei.c:479 ovl_check_origin() warn: passing zero to 'PTR_ERR'
> fs/overlayfs/namei.c:581 ovl_index_upper() warn: passing zero to 'ERR_CAST'
>
> Fixes: ad1d615cec1c ("ovl: use directory index entries for consistency verification")
> Fixes: e8f9e5b780b0 ("ovl: verify directory index entries on mount")
> Signed-off-by: Charles Han <hanchunchao@...pur.com>
> ---
>  fs/overlayfs/namei.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 0b8b28392eb7..bc917b56e2b1 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -475,7 +475,9 @@ static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
>         struct ovl_fh *fh = ovl_get_fh(ofs, upperdentry, OVL_XATTR_ORIGIN);
>         int err;
>
> -       if (IS_ERR_OR_NULL(fh))
> +       if (!fh)
> +               return -ENODATA;

Not good. This is changing behavior.

> +       else if (IS_ERR(fh))
>                 return PTR_ERR(fh);

PTR_ERR_OR_ZERO if you must.

>
>         err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
> @@ -577,7 +579,9 @@ struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index,
>                 return dget(index);
>
>         fh = ovl_get_fh(ofs, index, OVL_XATTR_UPPER);
> -       if (IS_ERR_OR_NULL(fh))
> +       if (!fh)
> +               return ERR_PTR(-ENODATA);
> +       else if (IS_ERR(fh))
>                 return ERR_CAST(fh);

I don't see what's wrong with casting a NULL pointer.
This looks like a dubious smatch warning.

We could add ERR_OR_NULL_CAST() but it seems pointless.

Thanks,
Amir.