linux-kernel - Re: [PATCH] ovl: inode reference leak in "ovl_is

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Date:   Mon, 15 Jun 2020 19:45:57 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     youngjun <her0gyugyu@...il.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ovl: inode reference leak in "ovl_is_inuse" true case.

On Mon, Jun 15, 2020 at 6:57 PM youngjun <her0gyugyu@...il.com> wrote:
>
> When "ovl_is_inuse" true case, trap inode reference not put.
>
> Signed-off-by: youngjun <her0gyugyu@...il.com>

Fixes: 0be0bfd2de9d ("ovl: fix regression caused by overlapping layers
detection")
Cc: <stable@...r.kernel.org> # v4.19+
Reviewed-by: Amir Goldstein <amir73il@...il.com>


> ---
>  fs/overlayfs/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 91476bc422f9..8837fc1ec3be 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1499,8 +1499,10 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>
>                 if (ovl_is_inuse(stack[i].dentry)) {
>                         err = ovl_report_in_use(ofs, "lowerdir");
> -                       if (err)
> +                       if (err) {
> +                               iput(trap);
>                                 goto out;
> +                       }
>                 }
>

Urgh! I moved this ovl_is_inuse() after ovl_setup_trap() for a reason, but I did
not explain why. While we are fixing the bug, it would be nice to add a comment
above ovl_setup_trap():

/*
 * Check if lower root conflicts with this overlay layers before checking
 * if it is in-use as upperdir/workdir of "another" mount, because we do
 * not bother to check in ovl_is_inuse() if the upperdir/workdir is in fact
 * in-use by our upperdir/workdir.
 */

Thanks,
Amir.