block: fix use after free in __blkdev_direct_IO

We can't dereference the dio structure after submitting the last bio for
this request, as I/O completion might have happened before the code is
run. Introduce a local is_sync variable instead.

Fixes: 542ff7bf ("block: new direct I/O implementation")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Matias Bjørling <m@bjorling.me>
Tested-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5db5d1340d69..3c47614a4b32 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -331,7 +331,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
         struct blk_plug plug;
         struct blkdev_dio *dio;
         struct bio *bio;
-        bool is_read = (iov_iter_rw(iter) == READ);
+        bool is_read = (iov_iter_rw(iter) == READ), is_sync;
         loff_t pos = iocb->ki_pos;
         blk_qc_t qc = BLK_QC_T_NONE;
         int ret;
@@ -344,7 +344,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
         bio_get(bio); /* extra ref for the completion handler */
 
         dio = container_of(bio, struct blkdev_dio, bio);
-        dio->is_sync = is_sync_kiocb(iocb);
+        dio->is_sync = is_sync = is_sync_kiocb(iocb);
         if (dio->is_sync)
                 dio->waiter = current;
         else
@@ -398,7 +398,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
         }
         blk_finish_plug(&plug);
 
-        if (!dio->is_sync)
+        if (!is_sync)
                 return -EIOCBQUEUED;
 
         for (;;) {