On 09/10/2018 17:19, Laurent Vivier wrote:
> 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.
Perhaps it could be reasonable to return &init_binfmt_ns rather than
NULL in this case?
Thanks,
Laurent
