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    SubjectRe: usercopy whitelist woe in scsi_sense_cache
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    On 4/17/18 5:06 PM, Kees Cook wrote:
    > On Tue, Apr 17, 2018 at 3:57 PM, Jens Axboe <axboe@kernel.dk> wrote:
    >> On 4/17/18 3:48 PM, Jens Axboe wrote:
    >>> On 4/17/18 3:47 PM, Kees Cook wrote:
    >>>> On Tue, Apr 17, 2018 at 2:39 PM, Jens Axboe <axboe@kernel.dk> wrote:
    >>>>> On 4/17/18 3:25 PM, Kees Cook wrote:
    >>>>>> On Tue, Apr 17, 2018 at 1:46 PM, Kees Cook <keescook@chromium.org> wrote:
    >>>>>>> I see elv.priv[1] assignments made in a few places -- is it possible
    >>>>>>> there is some kind of uninitialized-but-not-NULL state that can leak
    >>>>>>> in there?
    >>>>>>
    >>>>>> Got it. This fixes it for me:
    >>>>>>
    >>>>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
    >>>>>> index 0dc9e341c2a7..859df3160303 100644
    >>>>>> --- a/block/blk-mq.c
    >>>>>> +++ b/block/blk-mq.c
    >>>>>> @@ -363,7 +363,7 @@ static struct request *blk_mq_get_request(struct
    >>>>>> request_queue *q,
    >>>>>>
    >>>>>> rq = blk_mq_rq_ctx_init(data, tag, op);
    >>>>>> if (!op_is_flush(op)) {
    >>>>>> - rq->elv.icq = NULL;
    >>>>>> + memset(&rq->elv, 0, sizeof(rq->elv));
    >>>>>> if (e && e->type->ops.mq.prepare_request) {
    >>>>>> if (e->type->icq_cache && rq_ioc(bio))
    >>>>>> blk_mq_sched_assign_ioc(rq, bio);
    >>>>>> @@ -461,7 +461,7 @@ void blk_mq_free_request(struct request *rq)
    >>>>>> e->type->ops.mq.finish_request(rq);
    >>>>>> if (rq->elv.icq) {
    >>>>>> put_io_context(rq->elv.icq->ioc);
    >>>>>> - rq->elv.icq = NULL;
    >>>>>> + memset(&rq->elv, 0, sizeof(rq->elv));
    >>>>>> }
    >>>>>> }
    >>>>>
    >>>>> This looks like a BFQ problem, this should not be necessary. Paolo,
    >>>>> you're calling your own prepare request handler from the insert
    >>>>> as well, and your prepare request does nothing if rq->elv.icq == NULL.
    >>>>
    >>>> I sent the patch anyway, since it's kind of a robustness improvement,
    >>>> I'd hope. If you fix BFQ also, please add:
    >>>
    >>> It's also a memset() in the hot path, would prefer to avoid that...
    >>> The issue here is really the convoluted bfq usage of insert/prepare,
    >>> I'm sure Paolo can take it from here.
    >>
    >> Does this fix it?
    >>
    >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
    >> index f0ecd98509d8..d883469a1582 100644
    >> --- a/block/bfq-iosched.c
    >> +++ b/block/bfq-iosched.c
    >> @@ -4934,8 +4934,11 @@ static void bfq_prepare_request(struct request *rq, struct bio *bio)
    >> bool new_queue = false;
    >> bool bfqq_already_existing = false, split = false;
    >>
    >> - if (!rq->elv.icq)
    >> + if (!rq->elv.icq) {
    >> + rq->elv.priv[0] = rq->elv.priv[1] = NULL;
    >> return;
    >> + }
    >> +
    >> bic = icq_to_bic(rq->elv.icq);
    >>
    >> spin_lock_irq(&bfqd->lock);
    >
    > It does! Excellent. :)

    Sweet! I'll add a comment and queue it up for 4.17 and mark for stable, with
    your annotations too.

    --
    Jens Axboe

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