在 2018年4月14日，下午4:29，Amir Goldstein <amir73il@xxxxxxxxx> 写道：
>
> 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.
Indeed, just calling ovl_config_opt_neq() without checking return code will be fine.
However, I plan to return error when failing from ovl_parse_opt(), in another word,
if user specifies unrecognized or invalid options then return -EINVAL.
I also need to add a check for xino.
Thanks,
Chengguang.
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