On Sat, Apr 14, 2018 at 9:35 AM, Chengguang Xu <cgxu519@xxxxxxx> wrote:
> Check remount options and print warning if there is any unchangeable
> option.
>
> Signed-off-by: Chengguang Xu <cgxu519@xxxxxxx>
> ---
> Changes since v4:
> - Only print warning when detecting unchangeable options in remount.
> - Add validation of option 'default_permissions'.
> - Fix potential memleak in ovl_remount().
>
> Changes since v3:
> - Fix error prone macro helper.
> - Make another new patch to only include code around.
>
> Changes since v2:
> - Introduce two macro helpers to simplify remount option validation.
>
> Changes since v1:
> - Refactor ovl_free_fs(), move config freeing operations to ovl_free_config().
>
> fs/overlayfs/super.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 71 insertions(+), 5 deletions(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 0293635a..5fa1e6e 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -230,6 +230,14 @@ static void ovl_destroy_inode(struct inode *inode)
> call_rcu(&inode->i_rcu, ovl_i_callback);
> }
>
> +static void ovl_free_config(struct ovl_config *config)
> +{
> + kfree(config->lowerdir);
> + kfree(config->upperdir);
> + kfree(config->workdir);
> + kfree(config->redirect_mode);
> +}
> +
> static void ovl_free_fs(struct ovl_fs *ofs)
> {
> unsigned i;
> @@ -249,10 +257,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
> kfree(ofs->lower_layers);
> kfree(ofs->lower_fs);
>
> - kfree(ofs->config.lowerdir);
> - kfree(ofs->config.upperdir);
> - kfree(ofs->config.workdir);
> - kfree(ofs->config.redirect_mode);
> + ovl_free_config(&ofs->config);
> if (ofs->creator_cred)
> put_cred(ofs->creator_cred);
> kfree(ofs);
> @@ -542,14 +547,75 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
> return ovl_parse_redirect_mode(config);
> }
>
> +static bool ovl_opt_bool_neq(bool new, bool old, const char *name)
> +{
> + if (new != old) {
> + pr_err("overlayfs: option \"%s\" cannot be %s on remount.\n",
pr_warn("overlayfs: option \"%s\" cannot be %s on
remount, ignore.\n",
> + name, new ? "enabled" : "disabled");
> + return true;
> + }
> + return false;
> +}
> +
> +static bool ovl_opt_string_neq(const char *new, const char *old,
> + const char *name)
> +{
> + if (new && (!old || strcmp(new, old))) {
> + pr_err("overlayfs: option \"%s\" cannot be changed on remount.\n",
> + name);
> + return true;
> + }
> + return false;
> +}
> +
> +#define ovl_config_opt_neq(old, new, name, type) \
> + ovl_opt_##type##_neq((old)->name, (new)->name, #name)
> +
> +/*
> + * In current stage we only print warning message but not return error code
> + * when detecting the behavior of setting new value to unchangeable options.
> + */
> static int ovl_remount(struct super_block *sb, int *flags, char *data)
> {
> struct ovl_fs *ofs = sb->s_fs_info;
> + struct ovl_config *oc = &ofs->config;
> + struct ovl_config *nc;
> + int err;
>
> if (!(*flags & SB_RDONLY) && ovl_force_readonly(ofs))
> return -EROFS;
>
> - return 0;
> + nc = kzalloc(sizeof(struct ovl_config), GFP_KERNEL);
> + if (!nc)
> + return -ENOMEM;
> +
> + nc->index = oc->index;
> + nc->nfs_export = oc->nfs_export;
> + nc->default_permissions = oc->default_permissions;
> +
> + err = ovl_parse_opt((char *)data, nc);
> + if (err)
> + goto out_err;
> +
> + if (ovl_config_opt_neq(nc, oc, index, bool))
> + goto out_err;
No point in goto out_err if not aborting remount.
Amir.
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