Le 09/10/2018 à 17:16, Tycho Andersen a écrit :
> On Tue, Oct 09, 2018 at 12:37:52PM +0200, Laurent Vivier wrote:
>> @@ -80,18 +74,32 @@ static int entry_count;
>> */
>> #define MAX_REGISTER_LENGTH 1920
>>
>> +static struct binfmt_namespace *binfmt_ns(struct user_namespace *ns)
>> +{
>> + struct binfmt_namespace *b_ns;
>> +
>> + while (ns) {
>> + b_ns = READ_ONCE(ns->binfmt_ns);
>> + if (b_ns)
>> + return b_ns;
>> + ns = ns->parent;
>> + }
>> + WARN_ON_ONCE(1);
>
> It looks like we warn here,
>
>> @@ -133,17 +141,18 @@ static int load_misc_binary(struct linux_binprm *bprm)
>> struct file *interp_file = NULL;
>> int retval;
>> int fd_binary = -1;
>> + struct binfmt_namespace *ns = binfmt_ns(current_user_ns());
>>
>> retval = -ENOEXEC;
>> - if (!enabled)
>> + if (!ns->enabled)
>
> ...but then in cases like this we immediately dereference the pointer
> anyways and crash. Can we return some other error code here in the !ns
> case so we don't crash?
My concern here is I don't want to add code to check an error case that
cannot happen. The first namespace binfmt_ns pointer is initialized with
&init_binfmt_ns, so the return value cannot be NULL.
Thanks,
Laurent
