[Devel] [PATCH] binfmt_misc: fix mount after umount in CT

[Nikita Yushchenko]

It shall be [PATCH vz8] - sorry for missing that.

> vz7/vz8/vz9?
> 
> -- 
> Best regards,
> 
> Konstantin Khorenko,
> Virtuozzo Linux Kernel Team
> 
> On 18.10.2021 19:51, Nikita Yushchenko wrote:
>> The assumption that bm_fill_super() is not called for the second time
>> for CT is wrong: umount operation clears sb->s_root, which causes
>> vfs_get_super() to call fill_super again on the next mount.
>>
>> Make bm_fill_super() handle multiple-calls corrently:
>> - initialize bm_data and set ve->binfmt_misc only if it is not done
>>    before,
>> - delay desctruction of it up to CT destruction.
>>
>> https://jira.sw.ru/browse/PSBM-133968
>> Fixes: 8250ff41d190 ("ve/fs/binfmt: clean bm_data reference from ve on err path")
>> Signed-off-by: Nikita Yushchenko <nikita.yushchenko at virtuozzo.com>
>> ---
>>   fs/binfmt_misc.c | 37 +++++++++++++------------------------
>>   1 file changed, 13 insertions(+), 24 deletions(-)
>>
>> diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
>> index 0946e7e6caa5..5f4e90c1ade2 100644
>> --- a/fs/binfmt_misc.c
>> +++ b/fs/binfmt_misc.c
>> @@ -853,38 +853,25 @@ static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
>>       };
>>       struct ve_struct *ve = get_exec_env();
>> -    struct binfmt_misc *bm_data;
>> +    struct binfmt_misc *bm_data = ve->binfmt_misc;
>> -    /*
>> -     * bm_get_tree()
>> -     *  get_tree_keyed(fc, bm_fill_super, get_ve(ve))
>> -     *   fc->s_fs_info = current VE
>> -     *   vfs_get_super(fc, vfs_get_keyed_super, bm_fill_super)
>> -     *    sb = sget_fc(fc, test, set_anon_super_fc)
>> -     *    if (!sb->s_root) {
>> -     *        err = bm_fill_super(sb, fc);
>> -     *
>> -     * => we should never get here with initialized ve->binfmt_misc.
>> -     */
>> -    if (WARN_ON_ONCE(ve->binfmt_misc))
>> -        return -EEXIST;
>> +    if (!bm_data) {
>> +        bm_data = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);
>> +        if (!bm_data)
>> +            return -ENOMEM;
>> -    bm_data = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);
>> -    if (!bm_data)
>> -        return -ENOMEM;
>> +        INIT_LIST_HEAD(&bm_data->entries);
>> +        rwlock_init(&bm_data->entries_lock);
>> -    INIT_LIST_HEAD(&bm_data->entries);
>> -    rwlock_init(&bm_data->entries_lock);
>> +        ve->binfmt_misc = bm_data;
>> +        /* this will be cleared by ve_binfmt_fini() */
>> +    }
>>       err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
>> -    if (err) {
>> -        kfree(bm_data);
>> +    if (err)
>>           return err;
>> -    }
>>       sb->s_op = &s_ops;
>> -
>> -    ve->binfmt_misc = bm_data;
>>       bm_data->enabled = 1;
>>       return 0;
>> @@ -971,6 +958,8 @@ static void ve_binfmt_fini(void *data)
>>       while (!list_empty(&bm_data->entries))
>>           kill_node(bm_data, list_first_entry(
>>               &bm_data->entries, Node, list));
>> +
>> +    kfree(bm_data);
>>   }
>>   static struct ve_hook ve_binfmt_hook = {
>>