On 2/26/19 6:21 PM, Ming Lei wrote:
> On Tue, Feb 26, 2019 at 11:56 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>>
>> On 2/25/19 9:34 PM, Jens Axboe wrote:
>>> On 2/25/19 8:46 PM, Eric Biggers wrote:
>>>> Hi Jens,
>>>>
>>>> On Thu, Feb 21, 2019 at 10:45:27AM -0700, Jens Axboe wrote:
>>>>> On 2/20/19 3:58 PM, Ming Lei wrote:
>>>>>> On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote:
>>>>>>> For an ITER_BVEC, we can just iterate the iov and add the pages
>>>>>>> to the bio directly. This requires that the caller doesn't releases
>>>>>>> the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that.
>>>>>>>
>>>>>>> The current two callers of bio_iov_iter_get_pages() are updated to
>>>>>>> check if they need to release pages on completion. This makes them
>>>>>>> work with bvecs that contain kernel mapped pages already.
>>>>>>>
>>>>>>> Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
>>>>>>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>>>>>>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>>>>>>> ---
>>>>>>> block/bio.c | 59 ++++++++++++++++++++++++++++++++-------
>>>>>>> fs/block_dev.c | 5 ++--
>>>>>>> fs/iomap.c | 5 ++--
>>>>>>> include/linux/blk_types.h | 1 +
>>>>>>> 4 files changed, 56 insertions(+), 14 deletions(-)
>>>>>>>
>>>>>>> diff --git a/block/bio.c b/block/bio.c
>>>>>>> index 4db1008309ed..330df572cfb8 100644
>>>>>>> --- a/block/bio.c
>>>>>>> +++ b/block/bio.c
>>>>>>> @@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page,
>>>>>>> }
>>>>>>> EXPORT_SYMBOL(bio_add_page);
>>>>>>>
>>>>>>> +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
>>>>>>> +{
>>>>>>> + const struct bio_vec *bv = iter->bvec;
>>>>>>> + unsigned int len;
>>>>>>> + size_t size;
>>>>>>> +
>>>>>>> + len = min_t(size_t, bv->bv_len, iter->count);
>>>>>>> + size = bio_add_page(bio, bv->bv_page, len,
>>>>>>> + bv->bv_offset + iter->iov_offset);
>>>>>>
>>>>>> iter->iov_offset needs to be subtracted from 'len', looks
>>>>>> the following delta change[1] is required, otherwise memory corruption
>>>>>> can be observed when running xfstests over loop/dio.
>>>>>
>>>>> Thanks, I folded this in.
>>>>>
>>>>> --
>>>>> Jens Axboe
>>>>>
>>>>
>>>> syzkaller started hitting a crash on linux-next starting with this commit, and
>>>> it still occurs even with your latest version that has Ming's fix folded in.
>>>> Specifically, commit a566653ab5ab80a from your io_uring branch with commit date
>>>> Sun Feb 24 08:20:53 2019 -0700.
>>>>
>>>> Reproducer:
>>>>
>>>> #define _GNU_SOURCE
>>>> #include <fcntl.h>
>>>> #include <linux/loop.h>
>>>> #include <sys/ioctl.h>
>>>> #include <sys/sendfile.h>
>>>> #include <sys/syscall.h>
>>>> #include <unistd.h>
>>>>
>>>> int main(void)
>>>> {
>>>> int memfd, loopfd;
>>>>
>>>> memfd = syscall(__NR_memfd_create, "foo", 0);
>>>>
>>>> pwrite(memfd, "\xa8", 1, 4096);
>>>>
>>>> loopfd = open("/dev/loop0", O_RDWR|O_DIRECT);
>>>>
>>>> ioctl(loopfd, LOOP_SET_FD, memfd);
>>>>
>>>> sendfile(loopfd, loopfd, NULL, 1000000);
>>>> }
>>>>
>>>>
>>>> Crash:
>>>>
>>>> page:ffffea0001a6aab8 count:0 mapcount:0 mapping:0000000000000000 index:0x0
>>>> flags: 0x100000000000000()
>>>> raw: 0100000000000000 ffffea0001ad2c50 ffff88807fca49d0 0000000000000000
>>>> raw: 0000000000000000 0000000000000000 00000000ffffffff
>>>> page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0)
>>>
>>> I see what this is, I'll cut a fix for this tomorrow.
>>
>> Folded in a fix for this, it's in my current io_uring branch and my for-next
>> branch.
>
> Hi Jens,
>
> I saw the following change is added:
>
> + if (size == len) {
> + /*
> + * For the normal O_DIRECT case, we could skip grabbing this
> + * reference and then not have to put them again when IO
> + * completes. But this breaks some in-kernel users, like
> + * splicing to/from a loop device, where we release the pipe
> + * pages unconditionally. If we can fix that case, we can
> + * get rid of the get here and the need to call
> + * bio_release_pages() at IO completion time.
> + */
> + get_page(bv->bv_page);
>
> Now the 'bv' may point to more than one page, so the following one may be
> needed:
>
> int i;
> struct bvec_iter_all iter_all;
> struct bio_vec *tmp;
>
> mp_bvec_for_each_segment(tmp, bv, i, iter_all)
> get_page(tmp->bv_page);
I guess that would be the safest, even if we don't currently have more
than one page in there. I'll fix it up.
--
Jens Axboe
