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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Wed, 3 Jun 2020 19:11:17 +0300
Message-ID: <CAOQ4uxhLW=MSk=RhUi51EdOticfk1i_pku6qjCp2QpwnpyL5sw@mail.gmail.com>
Subject: Re: [PATCH][next] ovl: fix null pointer dereference on null stack
 pointer on error return
To:     Colin King <colin.king@canonical.com>
Cc:     Miklos Szeredi <miklos@szeredi.hu>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        kernel-janitors@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, Jun 3, 2020 at 6:46 PM Colin King <colin.king@canonical.com> wrote:
>
> From: Colin Ian King <colin.king@canonical.com>
>
> There are two error return paths where the call to path_put is
> dereferencing the null pointer 'stack'.  Fix this by avoiding the
> error exit path via label 'out_err' that will lead to the path_put
> calls and instead just return the error code directly.
>
> Addresses-Coverity: ("Dereference after null check)"
> Fixes: 4155c10a0309 ("ovl: clean up getting lower layers")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>


Which branch is that based on?
Doesn't seem to apply to master nor next

> ---
>  fs/overlayfs/super.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 1094836f7e31..4be1b041b32c 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1594,20 +1594,18 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
>         unsigned int i;
>         struct ovl_entry *oe;
>
> -       err = -EINVAL;
>         if (!ofs->config.upperdir && numlower == 1) {
>                 pr_err("at least 2 lowerdir are needed while upperdir nonexistent\n");
> -               goto out_err;
> +               return ERR_PTR(-EINVAL);
>         } else if (!ofs->config.upperdir && ofs->config.nfs_export &&
>                    ofs->config.redirect_follow) {
>                 pr_warn("NFS export requires \"redirect_dir=nofollow\" on non-upper mount, falling back to nfs_export=off.\n");
>                 ofs->config.nfs_export = false;
>         }
>
> -       err = -ENOMEM;
>         stack = kcalloc(numlower, sizeof(struct path), GFP_KERNEL);
>         if (!stack)
> -               goto out_err;
> +               return ERR_PTR(-ENOMEM);
>
>         err = -EINVAL;
>         for (i = 0; i < numlower; i++) {
> --
> 2.25.1
>